# man vxintro
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NAME
     vxintro - introduction to Volume Manager utilities

SYNOPSIS
     vxassist, vxconfigd, vxdctl, vxdg, vxdisk,  vxedit,  vxinfo,
     vxiod,  vxmake,  vxmend,  vxplex,  vxprint, vxrecover, vxsd,
     vxstat, vxtrace, vxvol

DESCRIPTION
     The Volume Manager utilities provide a shell-level interface
     for use by system administrators and high-level applications
     and scripts to query and manipulate objects managed  through
     the VERITAS Volume Manager (VxVMO).

GLOSSARY
     concatenated plex
               A plex whose subdisks are associated  at  specific
               offsets  within the address range of the plex, and
               extend into the plex address range for the  length
               of the subdisk.  This layout allows regions of one
               or more disks to create a plex, rather than a sin-
               gle big region.

     disk      Disks exist as two entities.  One is the  physical
               disk  on  which  all data is ultimately stored and
               which exhibits all the behaviors of the underlying
               technology.   The  other  is  the  Volume  Manager
               presentation of disks which,  while  mapping  one-
               to-one with the physical disks, are just presenta-
               tions of units from which allocations  of  storage
               are made.  As an example, a physical disk presents
               the image of a device with  a  definable  geometry
               with  a  definable number of cylinders, heads etc.
               whereas a Volume Manager disk is simply a unit  of
               allocation with a name and a size.

     disk access record
               A configuration record that defines a pathway to a
               disk.   The disk access records most commonly name
               a particular controller  number,  target  ID,  and
               logical  unit number.  The list of all disk access
               records stored in a system is  used  to  find  all
               disks attached to the system.  Disk access records
               do not identify particular physical disks.

               Disk access records are identified by  their  disk
               access names (also known as DA names).

               Through the use of disk IDs,  the  Volume  Manager
               allows  disks  to be moved between controllers, or
               to different locations on a  controller.   When  a
               disk is moved, a different disk access record will

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               be used when accessing the disk, although the disk
               media  record  will  continue  to track the actual
               physical disk.

               On some systems, the Volume Manager will  build  a
               list  of  disk access records automatically, based
               on the list of all devices attached to the system.
               On  these  systems,  it is not necessary to define
               disk access records explicitly.  On other systems,
               disk  access  records  must  be defined explicitly
               with the vxdisk define operation.  Specialty disks
               (such  as RAM disks or floppy disks) are likely to
               require explicit vxdisk define operations  on  all
               systems.

     disk group
               A group of disks that share  a  common  configura-
               tion.   A  configuration  consists  of  a  set  of
               records  describing  objects   (including   disks,
               volumes, plexes, and subdisks) that are associated
               with one particular disk group.  Each  disk  group
               has  an  administrator-assigned  name  that can be
               used by the administrator to reference  that  disk
               group.   Each disk group has an internally defined
               unique disk group ID, which is used  to  differen-
               tiate    two    disk    groups   with   the   same
               administrator-assigned name.

               Disk groups provide a method to partition the con-
               figuration  database, so that the database size is
               not too large and so that  database  modifications
               do  not  affect  too many drives.  They also allow
               the Volume Manager to operate with groups of  phy-
               sical  disk  media  that can be moved between sys-
               tems.

               Disks and disk groups have  a  circular  relation-
               ship:  disk groups are formed from disks, and disk
               group configurations are  stored  on  disks.   All
               disks  in  a  disk  group  are stamped with a disk
               group ID, which is a unique identifier for  naming
               disk  groups.   Some  or all disks in a disk group
               also store copies of the configuration database of
               the disk group.

     disk group configuration
               A disk group configuration  is  a  small  database
               that  contains all volume, plex, subdisk, and disk
               media records.  These  configurations  are  repli-
               cated  onto  some  or all disks in the disk group,
               usually with one copy on each disk.  Because these
               databases  are  stored  within disk groups, record

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               associations cannot span  disk  groups.   Thus,  a
               subdisk defined on a disk in one disk group cannot
               be associated with a volume in another disk group.

     disk header
               A block stored in a private region of a  disk  and
               that  defines several properties of the disk.  The
               disk  header  defines  the  size  of  the  private
               region,  the  location  and  size  of  the  public
               region, the unique disk ID for the disk, the  disk
               group  ID  and  disk  group  name  (if the disk is
               currently associated with a disk group),  and  the
               host  ID  for a host that has exclusive use of the
               disk.

     disk ID   A 64-byte universally unique  identifier  that  is
               assigned  to  a  physical  disk  when  its private
               region is initialized with the vxdisk init  opera-
               tion.   The  disk  ID  is stored in the disk media
               record so that the physical disk can be related to
               the disk media record at system startup.

     disk media record
               A reference to a physical disk or a disk partition
               This  record  can be thought of as a physical disk
               identifier for the disk or  partition  Disk  media
               records  are  configuration records that provide a
               name (known as the disk media  name  or  DM  name)
               that  you  can use to reference a particular disk,
               independent of its location on the system's  vari-
               ous  disk  controllers.  Disk media records refer-
               ence particular physical disks through a disk  ID,
               which is a unique identifier that is assigned to a
               disk when it  is  initialized  for  use  with  the
               Volume Manager.

               Operations are provided to set or remove the  disk
               ID stored in a disk media record.  Such operations
               have the effect of removing  or  replacing  disks,
               with  any  associated  subdisks  being  removed or
               replaced along with the disk.

     host ID   A name, usually  assigned  by  the  administrator,
               that  identifies  a particular host.  Host IDs are
               used to assign ownership  to  particular  physical
               disks.   When  a disk is part of a disk group that
               is in active use by a particular host, the disk is
               stamped with that host's host ID.  If another sys-
               tem attempts to access the disk,  it  will  detect
               that  the disk has a non-matching host ID and will
               disallow access until the first system  discontin-
               ues use of the disk.  To allow for system failures

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               that do not clear the host ID, the vxdisk clearim-
               port  operation  can  be used to clear the host ID
               stored on a disk.

               If a disk is a member of a disk group  and  has  a
               host  ID that matches a particular host, then that
               host will import the disk group as part of  system
               startup.

     kernel log
               A log kept in the private region on the  disk  and
               that is written by the Volume Manager kernel.  The
               log  contains  records  describing  the  state  of
               volumes  in  the  disk group.  This log provides a
               mechanism for the kernel to persistently  register
               state  changes so that vxconfigd can be guaranteed
               to detect the state changes even in the event of a
               system failure.

     plex      A copy of a volume's logical data  address  space,
               also  called a mirror.  A volume can have up to 32
               plexes associated with it.  Each plex is, at least
               conceptually,  a  copy of the volume that is main-
               tained consistently in the presence of volume  I/O
               and  reconfigurations.   Plexes represent the pri-
               mary means of configuring storage  for  a  volume.
               Plexes can have a striped, concatenated, or RAID-5
               organization (layout).

     plex consistency
               If the plexes of a volume contain different  data,
               then the plexes are said to be inconsistent.  This
               is only a problem if the Volume Manager is unaware
               of  the  inconsistencies, as the volume can return
               differing results  for  consecutive  reads.   Plex
               inconsistency  is  a  serious  compromise  of data
               integrity.  This inconsistency can  be  caused  by
               write  operations  that start around the time of a
               system failure, if parts of the write complete  on
               one  plex  but  not the other.  Plexes can also be
               inconsistent after creation of a mirrored  volume,
               if  the  plexes are not first synchronized to con-
               tain the same data.  An important part  of  Volume
               Manager operation is ensuring that consistent data
               is  returned  to  any  application  that  reads  a
               volume.  This may require that plex consistency of
               a volume be ``recovered'' by copying data  between
               plexes  so  that  they  have  the  same  contents.
               Alternatively, the volume can be put into a  state
               such  that  reads  from one plex are automatically
               written back to the other plexes, thus making  the
               data consistent for that volume offset.

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     private region
               Disks used by the Volume Manager contain two  spe-
               cial  regions:  a  private  region  and  a  public
               region. Usually, each region is formed from a com-
               plete  partition of the disk; however, the private
               and public regions can be allocated from the  same
               partition.

               The private region of a disk contains various  on-
               disk  structures  that  are  used  by  the  Volume
               Manager  for  various  internal  purposes.    Each
               private  region  begins  with  a disk header which
               identifies the disk and its disk  group.   Private
               regions  can also contain copies of a disk group's
               configuration, and copies of the disk group's ker-
               nel log.

     public region
               The public region of a disk is the space  reserved
               for  allocating  subdisks.   Subdisks  are defined
               with offsets that are relative to the beginning of
               the  public region of a particular disk.  Only one
               contiguous region of  disk  can  form  the  public
               region for a particular disk.

     root disk group
               Each system requires one special disk group, named
               rootdg,  which  is  generally the default for most
               utilities.  In addition to  defining  the  regular
               disk  group information, the configuration for the
               root disk group (rootdg) contains  local  informa-
               tion  that is specific to a disk group and that is
               not intended to be movable between systems.

     striped plex
               A plex that scatters data evenly  across  each  of
               its  associated  subdisks.   A  plex has a charac-
               teristic number of stripe columns  (consisting  of
               associated  subdisks)  and a characteristic stripe
               unit size.  The stripe unit size defines how  data
               with  a  particular address is allocated to one of
               the associated subdisks.  Given a stripe unit size
               of  128  blocks, and two stripe columns, the first
               group of 128 blocks  would  be  allocated  to  the
               first  subdisk,  the  second  group  of 128 blocks
               would be allocated  to  the  second  subdisk,  the
               third  group  to  the first subdisk, again, and so
               on.

     subdisk   A region of storage allocated on a  disk  for  use
               with a volume.  Subdisks are associated to volumes
               through plexes.  One or more subdisks are laid out

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               to  form plexes based on the plex layout (striped,
               concatenated, or  RAID-5).  Subdisks  are  defined
               relative to disk media records.

     volboot file
               The volboot file is a special file (usually stored
               in  /etc/vx/volboot) that is used to bootstrap the
               root disk group and to define a system's host  ID.
               In  addition  to  a host ID, the volboot file con-
               tains a list of disk access  records.   On  system
               startup,  this  list of disks is scanned to find a
               disk that is a member of the rootdg disk group and
               that  is stamped with this system's host ID.  When
               such a disk is found, its  configuration  is  read
               and  is  used  to get a more complete list of disk
               access records that are  used  as  a  second-stage
               bootstrap  of  the  root disk group, and to locate
               all other disk groups.

     volume    A virtual disk device that looks  to  applications
               and  file  systems  like  a regular disk partition
               device.  Volumes  present  block  and  raw  device
               interfaces  that  are compatible in their use with
               disk partition devices.  However, a  volume  is  a
               virtual  device  that  can  be  mirrored,  spanned
               across  disk  drives,  moved  to   use   different
               storage,  and  striped  using  administrative com-
               mands.  The  configuration  of  a  volume  can  be
               changed,   using  the  Volume  Manager  utilities,
               without causing disruption to applications or file
               systems that are using the volume.

CONVENTIONS
     The VERITAS Volume Manager employs  certain  conventions  to
     provide  a  degree of similarity between various operations.
     The conventions are used in the following areas:

          o  Disk Group Selection

          o  Standard Length Numbers

          o  Command Syntax

Disk Group Selection
     Most commands operate upon only one disk group  per  invoca-
     tion.   Each  disk  group  has a separate configuration from

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     every other disk group and  it  is  possible  for  two  disk
     groups to contain two objects that have the same name.  This
     can happen, in particular, if a disk group is moved from one
     system  to another.  However, most utilities make no attempt
     to ensure that names between disk groups are unique, so name
     collisions can occur.

     System administrators  who  try  to  avoid  name  collisions
     should  be  able to use most of the utilities without having
     to  specify  disk  groups  except  when  creating   objects.
     Administrators  cannot  use  single-command invocations that
     reference objects in more than  one  disk  group,  but  disk
     groups  will  be  selected  automatically,  based on objects
     specified in the command.

     The standard rules that most commands use for selecting  the
     disk group for a command are as follows:

     o  Given a particular set of object names specified  on  the
        command,  look for the disk group of each object.  If all
        objects are in the same disk group, use that disk  group.
        If  any  named  object  is  not  unique  between all disk
        groups, and if one of those object names is  not  in  the
        rootdg disk group, then fail.

     o  To force use of a particular disk group, use -g diskgroup
        to  indicate  the  group.   Non-unique names do not cause
        errors when a disk group is  specified  explicitly.   The
        diskgroup  specification  is  either a disk group ID or a
        disk group name.

     o  A special case is provided for  the  rootdg  disk  group.
        Any set of objects in the rootdg disk group can be speci-
        fied without specifying -g  rootdg,  even  if  the  given
        object name is used in another disk group.

        If a set of object names is given on  the  command  line,
        and  if some are unique but some are not unique, then the
        command will still fail according  to  the  rules  listed
        above.

Standard Length Numbers
     Many basic properties of objects that  are  managed  by  the
     Volume Manager require specification of lengths, either as a
     pure object length or as an offset relative  to  some  other
     object.   The  Volume  Manager supports volume lengths up to
     2,147,483,647 disk sectors (one terabyte on  most  systems).
     Typing such large numbers, or even much smaller numbers, can

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     be annoying.  The Volume Manager provides a  uniform  syntax
     for  representing such numbers, and uses suffixes to provide
     convenient  multipliers.   Numbers  can  be   specified   in
     decimal, octal, or hexadecimal.  Also, numbers can be speci-
     fied as a sum of several numbers, as a convenience to  avoid
     using a calculator.

     A hexadecimal (base 16) number is introduced using a  prefix
     of  0x.  For example, 0xfff is the same as decimal 4095.  An
     octal (base 8) number is introduced using  a  prefix  of  0.
     For example, 0177777 is the same as decimal 65535.

     A number can be followed by a suffix character to indicate a
     multiplier  for  the number.  A length number with no suffix
     character represents a count of standard disk sectors.   The
     length  of  a standard disk sector can vary between systems;
     it is commonly 512 bytes or 1024  bytes.  On  systems  where
     disks  can  have  different  sector sizes, one of the sector
     sizes will be chosen as the  ``standard''  size.   Supported
     suffix characters are:

          b    Multiply the length by 512 bytes (blocks)

          s    Multiply the length by the  standard  sector  size
               (default)

          k    Multiply the length by 1024 bytes (Kilobytes)

          m    Multiply the length  by  1,048,576  (1024K)  bytes
               (Megabytes)

          g    Multiply the length by 1,073,741,824 (1024M) bytes
               (Gigabytes)

     Numbers are represented internally as an integer  number  of
     sectors.   As  a result, if the standard disk sector size is
     larger than 512 bytes, numbers can be  specified  that  will
     need  to be rounded to a sector.  Rounding is always done to
     the next lowest, not the nearest,  multiple  of  the  sector
     size.

     Because the letter b is a valid hexadecimal character, there
     is  a  special  case  for  the b suffix where a single blank
     character can separate a number from the b suffix character.
     Use  of a blank within a number, when invoking commands from
     the shell, usually requires quoting the number.   For  exam-
     ple:

          vxassist make vol01 "0x1000 b"

     Numbers can be added or subtracted by separating two or more
     numbers  by a plus or minus sign, respectively.  A plus sign

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     is optional.  As an example, the largest allowed number that
     can  be  represented on a system with a 512 byte sector size
     can be entered as:

          1023g+1023m+1023k+1

     Note that 1024g-1 cannot be used, because the implementation
     cannot  handle  the  intermediate  representation  of  1024g
     (which is greater  than  the  largest  number  that  can  be
     represented) internally.

     In output, the Volume Manager reports length  numbers  as  a
     simple count of sectors, with no suffix character.

     Case  is  ignored  in  length  specification.    Hexadecimal
     numbers  and  suffix  characters  can be specified using any
     reasonable combination of uppercase and lowercase letters.

Utility Syntax
     Most utilities in the Volume Manager provide more  than  one
     operation,  with operations grouped into utilities primarily
     by object type.  Utilities that provide multiple  operations
     are typically invoked with the following form:

           utility_name [ options ] keyword [ operands ]

     utility_name is the name of the Volume Manager  command  and
     keyword  specifies  the  specific operation to perform.  Any
     options that are introduced in  the  standard  -letter  form
     precede  the  operation  keyword.   This  is in keeping with
     standard System V UNIX utility syntax, which provides for  a
     set of options as the first arguments to a command, followed
     by any non-option operands.  The keyword  is  considered  an
     operand under standard System V syntax.

     All of the utilities provide an extended usage message  that
     lists  all  the  options and operation keywords supported by
     the utility.  For utilities  that  are  keyword-based,  this
     extended  usage  message  can be displayed using the keyword
     help.  Utilities that use operands for purposes  other  than
     operation  selection  provide  a  reserved  option  of -H to
     display the extended usage information.

RECORD TYPES
     Disk group configurations contain six types of records:

          o  Disk Access Records

          o  Disk Group Records

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          o  Disk Media Records

          o  Plex Records

          o  Subdisk Records

          o  Volume Records

     Disk access records are specific to the root disk group  and
     are  stored in configurations only because there is no other
     convenient place to store them; otherwise,  they  are  logi-
     cally  separate  from  all  disk  groups.   Because they are
     specific and meaningful to the local system only, the  logi-
     cal  place for their storage is the rootdg since that is the
     only disk group guaranteed to exist on the system.

Disk Access Records
     Disk access records define an address, or access path,  that
     can  be  used to access a disk.  The list of all disk access
     records defines the list of  all  disk  addresses  that  the
     Volume  Manager  can  use  to  locate  physical disks.  Disk
     access records do not define specific physical disks,  since
     physical  disks  can  be moved on a system.  When a physical
     disk is moved, a different disk access record may be  neces-
     sary to locate it.

     Disk access records are stored in the rootdg disk group con-
     figuration.   Unlike  all  other  record types, the names of
     disk access records can conflict with  the  names  of  other
     records.  For example, a specialty disk (such as a RAM disk)
     can use the same name for both the disk  access  record  and
     the  disk  media  record that points to it.  It is typically
     advisable to use different names for the  access  and  media
     records, to avoid additional confusion if disks are moved.

     Disk access records can be defined explicitly.  Some  (some-
     times  all)  disk access records may be configured automati-
     cally by the Volume Manager, based on available  information
     in  the  operating  system.   Such  automatically-configured
     disks are not stored persistently in the on-disk  root  disk
     group  configuration, but are instead regenerated every time
     the Volume Manager starts up.

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     Disk access records have the  following  fundamental  attri-
     butes:

     disk access name
               The name of the disk access record is typically  a
               disk  address.   Disk  access names are usually of
               the form c#t#d#s2, indicating use  of  the  entire
               disk on controller c#, with SCSI target ID t#, and
               logical unit d#.  The s2 suffix is used as a  con-
               vention  indicating the use of standard partition-
               ing.  Other systems are likely to  have  different
               conventions for the disk access name.

     type      Each disk access record has a type, which  identi-
               fies  key  characteristics of the Volume Manager's
               interaction with the disk.  Available  types  are:
               sliced,  simple,  and  nopriv.  See vxdisk(1M) for
               more information on disk types.   Typically,  most
               or  all  of  the disks will be of type sliced.  It
               may be desirable to create specialty  disks  (such
               as RAM disks) with type nopriv.

     If the physical disk represented by the disk  access  record
     is  associated  with a disk media record, then the following
     fields are defined:

     disk group name
               The name of the disk  group  containing  the  disk
               media record.

     disk media name
               The name of the disk media record that  points  to
               the physical disk.

     Additional attributes can be  added,  arbitrarily,  by  disk
     types.   See  vxdisk(1M) for a list of additional attributes
     defined by the standard disk types.

Disk Group Records
     Disk group records define several different types  of  names
     for a disk group.  The different types of names are:

     alias name
               This is the standard name  that  the  system  uses
               when  referencing  the  disk group.  References to
               the disk group name usually mean the  alias  name.
               Volume  directories  are structured into subdirec-
               tories based on the disk group alias name.   Typi-
               cally,  the  disk group's alias name and real name
               are identical.  A local alias can  be  useful  for
               gaining  access  to  a disk group with a name that
               conflicts with other disk groups in the system, or

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               that  conflicts  with  records  in the rootdg disk
               group.

     disk group ID
               A 64-byte identifier that represents the unique ID
               of the disk group.  All disk groups on all systems
               should have a different disk  group  ID,  even  if
               they  have the same real name.  This identifier is
               stored in the disk headers of  all  disks  in  the
               disk  group.  It is used to ensure that the Volume
               Manager does not confuse  two  disk  groups  which
               were created with the same name.

     real name This is the name of the disk group, as defined  on
               disk.   This name is stored in the disk group con-
               figuration, and is also stored in the disk headers
               of all disks in the disk group.

Disk Media Records
     Disk media records define a  specific  disk  within  a  disk
     group.   The  name  of  a  disk media record (the disk media
     name) is assigned when a disk is first added to a disk group
     (using  the vxdg adddisk operation).  Disk media records can
     be assigned to specific physical disks  by  associating  the
     disk  media  record  with the current disk access record for
     the physical disk.

     Disk media records have  the  following  fundamental  attri-
     butes:

     disk access name
               The disk access name that  is  currently  used  to
               access  the  physical  disk referenced by the disk
               ID.  If the disk ID is defined,  but  no  physical
               disk  with that ID could be found, the disk access
               name will be clear.  A  disk  where  the  physical
               disk could not be found is considered to be in the
               NODAREC,  or  inaccessible,  state.   A  disk  can
               become  inaccessible  either because the indicated
               disk is not currently attached to the  system,  or
               because   I/O   failures   on  the  physical  disk
               prevented the Volume Manager from  identifying  or
               using the physical disk.

     disk ID   A 64-byte unique identifier representing the  phy-
               sical  disk  to  which the media record is associ-
               ated.  This can be cleared to  indicate  that  the
               disk  is  considered  in  the  removed  state.   A
               removed disk has no current association  with  any
               physical disk.

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     A disk media record that has an active  association  with  a
     physical  disk  (both  the  disk ID and the disk access name
     attributes are defined), inherits  several  properties  from
     the  underlying  physical  disk.  These attributes are taken
     from the disk header, which is stored in the private  region
     of the the disk.  These inherited attributes are:

     atomic I/O size
               This is the fundamental I/O size for the disk,  in
               bytes,  also  known  as the sector size.  All I/Os
               destined for this disk must be multiples  of  this
               size.  Currently, the Volume Manager requires that
               all disks have the same sector size.  On most sys-
               tems, this size is 512 bytes.

     private length
               The length of the region of the physical disk that
               is  reserved  for  storing  private Volume Manager
               information.

     public length
               The length of the region of the physical disk that
               is available for subdisk allocations.

Plex Records
     Plex records define the characteristics of a particular plex
     of a volume.  A plex can be in either an associated state or
     a dissociated state.  In the dissociated state, the plex  is
     not  a  part  of  a  volume.   A  dissociated plex cannot be
     accessed in any way.  An associated  plex  can  be  accessed
     through the volume.

     Plexes have the following fundamental attributes:

     comment   An administrator-assigned string of up to 40 char-
               acters  that  can  be  set  and  changed using the
               vxedit  utility.   The  Volume  Manager  does  not
               interpret  the  comment  field. The comment cannot
               contain newline characters.

     condition flags
               Various condition flags are defined for  the  plex
               that  define  state  which is recognized automati-
               cally, rather than managed  by  the  volume  usage
               type.  Defined flags are:

               IOFAIL    The plex was detached as a result of  an
                         I/O   failure   detected  during  normal
                         volume I/O.   The  plex  is  out-of-date
                         with  respect to the volume, and in need
                         of  complete  recovery.   However,  this
                         condition  also  indicates  a likelihood

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                         that one of  the  disks  in  the  system
                         should be replaced.

               NODAREC   No  physical   disk   could   be   found
                         corresponding to the disk ID in the disk
                         media record for  one  of  the  subdisks
                         associated with the plex.  The plex can-
                         not be used until the condition is fixed
                         or the affected subdisk is dissociated.

               RECOVER   A disk for one of the disk media records
                         was  replaced or was reattached too late
                         to prevent the plex from  becoming  out-
                         of-date with respect to the volume.  The
                         plex  requires  complete  recovery  from
                         another  plex in the volume to synchron-
                         ize the plex with the  correct  contents
                         of the volume.

               REMOVED   One of the disk media  records  was  put
                         into  the removed state through explicit
                         administrative action.  The plex  cannot
                         be  used  until  the disk is replaced or
                         the affected subdisk is dissociated.

     contiguous length
               The offset of the first block in the plex  address
               space  that  is  not  backed by a subdisk.  If the
               plex has no holes, the contiguous  length  matches
               the  plex  length.   If  the  contiguous length is
               equal to or greater than the length of the associ-
               ated volume, the plex is considered complete, oth-
               erwise it is sparse.

     I/O mode  Each plex is in read-write, read-only,  or  write-
               only  mode.   This  mode  affects  read  and write
               operations directed to the volume, if the plex  is
               enabled.   For  read-write  and  read-only  modes,
               volume read operations  can  be  directed  to  the
               plex.  For read-write and write-only modes, volume
               write operations are directed to the plex.

               Plexes are normally in  read-write  mode.   Write-
               only  mode  is used to recover a plex that failed,
               and whose contents have  thus  become  out-of-date
               with  respect to the volume.  It is also used when
               attaching a new plex to a volume.   In  write-only
               mode,  writes  to the volume will update the plex,
               causing written regions to be  up-to-date.   Typi-
               cally,  a  set  of special copy operations will be
               used to update the remainder of the plex.

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     layout    The  organization  of  associated  subdisks   with
               respect  to the plex address space.  The layout is
               striped, concatenated, or RAID-5.

     length    The length of a plex is the  offset  of  the  last
               subdisk  in  the plex plus the length of that sub-
               disk.  In other words, the length of the  plex  is
               defined  by  the  last  block  in the plex address
               space that is backed by a subdisk.  This value may
               or  may  not  relate  to the length of the volume,
               depending on whether the plex is  completely  con-
               tiguously allocated.

     log subdisk
               Each plex can have at most one associated log sub-
               disk.  A log subdisk is used with the dirty region
               logging feature to improve the  time  required  to
               recover  consistency  of  a  volume after a system
               failure.

     plex state
               Each  plex  is  either   enabled,   disabled,   or
               detached.   When  enabled,  normal  read and write
               operations from the volume can be directed to  the
               plex.   When  disabled,  no I/O operations will be
               applied to the plex.  When detached, normal volume
               I/O will not be directed to the plex.

               I/O failures encountered during normal volume  I/O
               may  move  the  enabled  state for a plex directly
               from enabled to detached.  See the description  of
               volume  exception policies (earlier in this manual
               page) for more information.

     subdisks  Each plex has zero or  more  associated  subdisks.
               Subdisks are associated at offsets relative to the
               beginning of the plex address space.  Subdisks for
               concatenated  plexes  may  not  cover  the  entire
               length of the plex, in which case they leave holes
               in  the  plex.   A plex that is not as long as the
               volume to which it is associated is considered  to
               have  a hole extending from the end of the plex to
               the end of the volume.  A plex with a hole is con-
               sidered   incomplete,   and  is  sometimes  called
               sparse.

     usage-type state
               Volume usage types maintain a private state  field
               related  to the the operations that have been per-
               formed on the plex, or to failure conditions  that
               have  been encountered.  This state field contains
               a string of up to 14 characters.

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     volatile state
               A plex is considered to have ``volatile'' contents
               if the disk for any of the plex's subdisks is con-
               sidered to be volatile.  The contents of  a  vola-
               tile  disk  are  not  presumed to survive a system
               reboot.  The  contents  of  a  volatile  plex  are
               always considered out-of-date after a recovery and
               in need of complete recovery from another plex.

Subdisk Records
     Subdisk records define a region of disk,  allocated  from  a
     disk's public region.  Subdisks have very little state asso-
     ciated with them, other than the  configuration  state  that
     defines which region of disk the subdisk occupies.  Subdisks
     cannot overlap each other, either in their associations with
     plexes, or in their arrangement on disk public regions.

     Subdisks have the following fundamental attributes:

     comment   An administrator-assigned string of up to 40 char-
               acters  that  can  be  set  and  changed using the
               vxedit  utility.   The  Volume  Manager  does  not
               interpret  the  comment  field. The comment cannot
               contain newline characters.

     disk media name
               The name of the disk media record that the subdisk
               is defined on.

     disk offset
               The offset, from the beginning of the disk's  pub-
               lic region, to the start of the subdisk.

     length    The length of the subdisk.

     plex offset
               For associated subdisks, this is the offset  (from
               the beginning of the plex) of the subdisk associa-
               tion.   For  subdisks  associated   with   striped
               plexes,  the plex offset defines relative ordering
               of  subdisks  in  the  plex,  rather  than  actual
               offsets within the plex address space.

Volume Records
     Volume records  define  the  characteristics  of  particular
     volume  devices.   The  name  of a volume record defines the
     node name used for files in the /dev/vx/dsk and /dev/vx/rdsk
     directories.   The  block  device  for  a  particular volume
     (which can be used as an argument to the mount command  (see
     mount(1M)) has the path:

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          /dev/vx/dsk/groupname/volume

     where groupname is the name assigned by the administrator to
     the  disk group containing the volume.  The raw device for a
     volume, typically used for application I/O and  for  issuing
     I/O control operations (see ioctl(2)), has the path:

          /dev/vx/rdsk/groupname/volume

     For convenience, volumes assigned to the root disk group are
     accessible  under  the  rootdg subdirectories of /dev/vx/dsk
     and /dev/vx/rdsk, but are also under /dev/vx/dsk/volume  and
     /dev/vx/rdsk/volume.

     Reads to a volume device are directed to one  of  the  read-
     write  or  read-only  plexes  associated  with  the  volume.
     Writes to the volume are directed  to  all  of  the  enabled
     read-write and write-only plexes associated with the volume.

     During a write operation, two plexes of a volume may  become
     out  of  sync  with  each other, due to the fact that writes
     directed to two disks can complete at different times.  This
     is  not  normally a problem.  However, if the system were to
     crash or lose power during a write operation, the two plexes
     could have different contents.

     Most applications and file systems are not written with  the
     presumption  that  two separate reads of a device can return
     different contents without an intervening  write  operation.
     Since  plexes  with  different  contents  could cause such a
     situation where two read operations of a block  return  dif-
     ferent  contents,  the  Volume  Manager expends considerable
     effort to ensure that this is avoided.

     Volumes have the following fundamental attributes:

     comment   An administrator-assigned string of up to 40 char-
               acters  that  can  be  set  and  changed using the
               vxedit  utility.   The  Volume  Manager  does  not
               interpret  the  comment field.  The comment cannot
               contain newline characters.

     exception policy
               There are several modes that can  be  set  on  the
               volume,  by  utilities according to the usage type
               of the volume.  These modes affect operation of  a
               volume in the presence of I/O failures.  Currently
               only one of these policies, called  GEN_DET_SPARSE
               is  ever  used.   This  policy tracks complete and
               incomplete plexes in a volume (an incomplete  plex
               does  not have a backing subdisk for all blocks in
               the volume).  If an unrecoverable error occurs  on

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               an incomplete plex, the plex is detached (disabled
               from receiving regular volume I/O  requests).   If
               an  unrecoverable error occurs on a complete plex,
               the plex is detached unless it is  the  last  com-
               plete  plex.   If  the  plex  is the last complete
               read-write plex, any incomplete plexes that  over-
               lap  with  the error will be detached but the plex
               with the error will remain attached.

               This default policy is chosen to  ensure  that  an
               I/O  that  fails  on  one  plex  will  not, in the
               future, be directed to that plex again unless that
               plex  is the last complete plex remaining attached
               to the volume.  In that case, the  policy  ensures
               that   the  volume  will  return  the  error  con-
               sistently, even  in  the  presence  of  incomplete
               plexes.

     length    Each volume has a length, which defines the limit-
               ing  offset  of  read  and  write operations.  The
               length is assigned by the administrator,  and  may
               or  may  not  match  the lengths of the associated
               plexes.

     log type  A policy to use for logging changes to the volume,
               which can be assigned by the administrator.  Poli-
               cies that can be specified are:

               none      Do not perform any special actions  when
                         writing  to  the volume.  Just write the
                         requested  data  to  all  read-write  or
                         write-only plexes.

               dirty-region-log
                         A volume is divided into regions. A bit-
                         map  where  each  bit  corresponds  to a
                         region is maintained. When a write to  a
                         particular region occurs, the respective
                         bit is set to on.  When  the  system  is
                         restarted  after  a  crash,  this region
                         bitmap is used to limit  the  amount  of
                         data copying that is required to recover
                         plex consistency for  the  volume.   The
                         region changes are logged to special log
                         subdisks associated  with  each  of  the
                         plexes  associated with the volume.  Use
                         of  dirty  region  logging  can  greatly
                         speed  recovery of a volume, but it also
                         degrades performance of the volume under
                         normal operation.

     plexes    Each volume has between  zero  and  32  associated

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               plexes.

     read policy
               A configurable policy for switching between plexes
               for volume reads.  When a volume has more than one
               enabled associated plex, the  Volume  Manager  can
               distribute  reads between the plexes to distribute
               the I/O load  and  thus  increase  total  possible
               bandwidth  of  reads through the volume.  The read
               policy can be set by the administrator.   Possible
               policies are:

               preferred plex
                         This read policy specifies a  particular
                         named  plex that is used to satisfy read
                         requests.  In  the  event  that  a  read
                         request  cannot be satisfied by the pre-
                         ferred  plex,  this  policy  changes  to
                         round-robin.

               round-robin
                         For every other read operation,  distri-
                         bute  the  operation  across  all of the
                         available plexes.  Given  three  plexes,
                         this  will  switch  between  each of the
                         three plexes,  so  each  plex  gets  one
                         third of the read requests.

               select    This read policy is the default  policy,
                         and  adjusts  to use an appropriate read
                         policy based on the set of plexes  asso-
                         ciated  with the volume.  If exactly one
                         enabled read-write striped plex is asso-
                         ciated  with  the volume, then that plex
                         is chosen automatically as the preferred
                         plex;  otherwise, the round-robin policy
                         is used.  If a volume  has  one  striped
                         plex  and  one non-striped plex, prefer-
                         ring  the  striped  plex  often   yields
                         better throughput.

     read/write-back recover mode
               This is a mode that applies to the  volume,  which
               is  managed  by  utilities  as  part  of plex con-
               sistency recovery.  When  this  mode  is  enabled,
               each  read operation will recover plex consistency
               for the region covered by  the  read.   Plex  con-
               sistency  is recovered by reading data from blocks
               of one plex and writing that  data  to  all  other
               writable  plexes.  This ensures that a future read
               operation covering the same range of  blocks  will
               read the same data.

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     start options
               This is a string that is organized  as  a  set  of
               usage-type  options  to  apply when starting (ena-
               bling) a volume.  See vxvol(1M) for details.

     usage type
               Each volume has a usage type, which defines a par-
               ticular  class  of  rules  for  operating  on  the
               volume, typically based on the expected content of
               the  volume.   Several  utilities can apply exten-
               sions or limitations that apply to volumes with  a
               particular  usage  type.  Several  usage types are
               included with  the  base  release  of  the  Volume
               Manager:  fsgen, for use with volumes that contain
               file systems; gen, for use with volumes  that  are
               used  as  swap  devices  or for other applications
               that do not use file systems; and special root and
               swap  usage  types  which are specifically for use
               with the root file system volume and  the  primary
               swap device.

     usage-type state
               Usage types maintain a private state field related
               to  the volume that relate to operations that have
               been performed on the volume, or to failure condi-
               tions  that  have  been  encountered.   This state
               field contains a string of up to 14 characters.

     user|group|mode
               These attributes are the  user,  group,  and  file
               permission modes used for the volume device nodes.
               The user and group are normally  root.   The  mode
               usually  allows  read  and write permission to the
               owner, and no access by other users.

     volume state
               Each  volume  is  either  enabled,  disabled,   or
               detached.   When  enabled,  normal  read and write
               operations are allowed on the volume, and any file
               system  residing  on the volume can be mounted, or
               used in the usual way.  When disabled,  no  access
               to  the  volume or any of its associated plexes is
               allowed.

     write-back-on-read-failure mode
               This is a mode that applies to the  volume,  which
               can  be  enabled  or disabled by the administrator
               using vxedit.  If this mode  is  enabled,  then  a
               read failure for a plex will cause data to be read
               from an alternate plex and then  written  back  to
               the  plex  that  got  the read failure.  This will
               usually fix the  error.   Only  if  the  writeback

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               fails  will  the  plex  be  detached for having an
               unrecoverable I/O failure.

     writecopy mode
               This is a mode that applies to the  volume,  which
               can  be  enabled  or disabled by the administrator
               using vxedit.  This  mode  takes  affect  only  if
               dirty  region  logging  is  in  effect.   When the
               operating system hands off a write request to  the
               volume  driver,  the operating system may continue
               to change the memory  that  is  being  written  to
               disk.   The  Volume Manager cannot detect that the
               memory is changing, so it can inadvertently  leave
               plexes  with  inconsistent  contents.  This is not
               normally a problem, because the  operating  system
               ensures that any such modified memory is rewritten
               to the volume before the volume is closed (such as
               by a clean system shutdown).  However, if the sys-
               tem crashes, plexes may  be  inconsistent.   Since
               the dirty region logging feature prevents recovery
               of the entire  volume,  it  may  not  ensure  that
               plexes are entirely consistent.

               Turning on the writecopy mode (which  is  normally
               set by default) often causes the Volume Manager to
               copy the data for a write request to a new section
               of  memory before writing it to disk.  Because the
               write is done from the copied  memory,  it  cannot
               change  and  so  the  data written to each plex is
               guaranteed to be the same if the write completes.

VOLUME USAGE TYPES
     The usage type of a volume represents a class of  rules  for
     operating  on a volume.  Each usage type is defined by a set
     of executables under the directory  /etc/vx/type/usage_type,
     where  usage_type  is the name given to the usage type.  The
     required executables are: vxinfo,  vxmake,  vxmend,  vxplex,
     vxsd,  and  vxvol.   These  executables  are  invoked by the
     Volume Manager administrative utilities with the same names.
     The  executables under /etc/vx/type should not, normally, be
     executed directly.

     Five usage types are provided with the Volume Manager:  gen,
     fsgen,  root,  swap,  and  raid5.  It is possible for third-
     party products to install additional usage types.

     The usage types provided with the Volume Manager store state
     information  in the volume and plex usage-type state fields.
     The state fields defined for volumes are:

     ACTIVE    The volume has been started and  is  running  nor-
               mally, or was running normally when the system was

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               stopped.  If the system  crashes  in  this  state,
               then  the  volume  may  require  plex  consistency
               recovery.

     CLEAN     The volume has been stopped and the  contents  for
               all plexes are consistent.

     EMPTY     The volume is not yet initialized.   This  is  the
               initial state for volumes created by vxmake.

     NEEDSYNC  The volume requires recovery.  This  is  typically
               set  after  a  system failure to indicate that the
               plexes in the volume may be inconsistent, so  that
               they require recovery (see the resync operation in
               vxvol(1M)).

     SYNC      Plex consistency recovery is currently being  done
               on  the volume.  vxvol resync sets this state when
               it starts to recovery plex consistency on a volume
               that was in the NEEDSYNC state.

     The state fields defined for plexes are:

     ACTIVE    The plex is running normally on a started  volume.
               The   plex   condition  flags  (NODAREC,  REMOVED,
               RECOVER, and IOFAIL) may apply if  the  system  is
               rebooted and the volume restarted.

     CLEAN     The plex was running normally when the volume  was
               stopped.  The plex will be enabled without requir-
               ing recovery when the volume is started.

     EMPTY     The plex is not yet initialized.   This  state  is
               set when the volume state is also EMPTY.

     OFFLINE   The plex was disabled by the vxmend off operation.
               See vxmend(1M) for more information.

     SNAPATT   This is a snapshot plex that is being attached  by
               the vxassist snapstart operation.  When the attach
               is complete,  the  state  for  the  plex  will  be
               changed  to  SNAPDONE.  If the system fails before
               the attach completes, the plex and all of its sub-
               disks will be removed.

     SNAPDIS   This  is  a  snapshot  plex  created   by   vxplex
               snapstart  that is fully attached.  A plex in this
               state can be turned into a  snapshot  volume  with
               vxplex snapshot.  See vxplex(1M) for more informa-
               tion.  If the system fails before the attach  com-
               pletes,  the  plex  will  be  dissociated from the
               volume.

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     SNAPDONE  This  is  a  snapshot  plex  created  by  vxassist
               snapstart  that is fully attached.  A plex in this
               state can be turned into a  snapshot  volume  with
               vxassist  snapshot.   See  vxassist(1M)  for  more
               information.   If  the  system  fails  before  the
               attach completes, the plex and all of its subdisks
               will be removed.

     SNAPTMP   This is a snapshot  plex  being  attached  by  the
               vxplex  snapstart  operation.   When the attach is
               complete, the state for the plex will  be  changed
               to SNAPDIS.  If the system fails before the attach
               completes, the plex will be dissociated  from  the
               volume.

     STALE     The plex was detached, either by vxplex det or  by
               an I/O failure.  vxvol start will change the state
               for a plex to STALE if any of the  plex  condition
               flags  are  set.   STALE plexes will be reattached
               automatically, when starting a volume, by  calling
               vxplex att.

     TEMP      This is  a  plex  that  is  being  associated  and
               attached to a volume with vxplex att.  If the sys-
               tem fails before the  attach  completes  the  plex
               will be dissociated from the volume.

     TEMPRM    This is  a  plex  that  is  being  associated  and
               attached to a volume with vxplex att.  If the sys-
               tem fails before the  attach  completes  the  plex
               will  be  dissociated from the volume and removed.
               Any subdisks in the plex will be kept.

     TEMPRMSD  This is  a  plex  that  is  being  associated  and
               attached to a volume with vxplex att.  If the sys-
               tem fails before the attach  completes,  the  plex
               and  its  subdisks  will  be  dissociated from the
               volume and removed.

EXIT CODES
     The majority of the Volume Manager utilities  use  a  common
     set  of  exit  codes,  which can be used by shell scripts or
     other types  of  programs  to  react  to  specific  problems
     detected  by  the  utilities.  For C programmers, these exit
     status codes are defined in the  include  file  volclient.h.
     The  number  and  macro  name for each distinct exit code is
     described below.  Shell script writers must directly compare
     against the numbers specified.

     (0) VEX_OK
               The utility is not reporting any error through the
               exit code.

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     (1) VEX_USAGE
               Some command line arguments to  the  utility  were
               invalid.

     (2) VEX_SYNTAX
               A syntax error occurred in a command  or  descrip-
               tion,  or  a  specified record name is too long or
               contains  invalid  characters.    This   code   is
               returned  only  by utilities that implement a com-
               mand or description language.  This code may  also
               be returned for errors in search patterns.

     (3) VEX_NOVOLD
               The volume daemon does not appear to be running.

     (4) VEX_IPC
               An unexpected error was encountered while communi-
               cating with the volume daemon.

     (5) VEX_OSERR
               An unexpected error was returned by a system  call
               or  by the C library.  This can also indicate that
               the utility ran out of memory.

     (6) VEX_LOST
               The status for  a  commit  was  lost  because  the
               volume  daemon was killed and restarted during the
               commit of a transaction,  but  after  restart  the
               volume daemon did not know whether the commit suc-
               ceeded or failed.

     (7) VEX_UTILERR
               The utility encountered an error  that  it  should
               not  have  encountered.   This generally implies a
               condition that the utility should have tested  for
               but  did not, or a condition that results from the
               volume daemon returning a value that did not  make
               sense.

     (8) VEX_TIMEOUT
               The  time  required  to  complete  a   transaction
               exceeded 60 seconds, causing the transaction locks
               to be lost.  As most utilities will reattempt  the
               transaction  at  least  once  if a timeout occurs,
               this usually implies that a transaction timed  out
               two or more times.

     (9) VEX_NODG
               No disk group could be identified  for  an  opera-
               tion.   This  results  either  from  naming a disk
               group that does not exist, or from supplying names
               on  a  command  line  that  are  in different disk

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               groups or in multiple disk groups.

     (10) VEX_CHANGED
               A change made to the database by  another  process
               caused  the  utility  to  stop.  This code is also
               returned by a usage-type-dependent utility  if  it
               is  given  a record that is associated with a dif-
               ferent usage type.  If this situation occurs  when
               the  usage-type-dependent utility is called from a
               switchout utility, then the database  was  changed
               after  the switchout utility determined the proper
               usage type to invoke.

     (11) VEX_NOENT
               A requested subdisk, plex, or  volume  record  was
               not found in the configuration database.  This may
               also mean that a record was an inappropriate type.

     (12) VEX_EXIST
               A name used to create a new  configuration  record
               matches the name of an existing record.

     (13) VEX_BUSY
               A subdisk, plex, or volume is locked against  con-
               current  access.   This  code  is  used for inter-
               transaction locks associated with usage type util-
               ities.   The code is also used for the dissociated
               plex or subdisk lock convention,  which  writes  a
               non-blank  string  to the tutil[0] field in a plex
               or subdisk structure to indicate that  the  record
               is being used.

     (14) VEX_NOUSETYPE
               No usage type could be determined  for  a  utility
               that requires a usage type.

     (15) VEX_BADUSETYPE
               An unknown or invalid usage type was specified.

     (16) VEX_ASSOC
               A plex or subdisk is associated, but the operation
               requires a dissociated record.

     (17) VEX_DISASSOC
               A plex or subdisk is dissociated, but  the  opera-
               tion requires an associated record.  This code can
               also be used to indicate that a subdisk or plex is
               not associated with a specific plex or volume.

     (18) VEX__LAST
               A plex or subdisk was not dissociated  because  it
               was  the  last  record associated with a volume or

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               plex.

     (19) VEX_TOOMANY
               Association of a plex or subdisk would surpass the
               maximum  number that can be associated to a volume
               or plex.

     (20) WVEX_INVAL
               A specified operation is invalid within the param-
               eters   specified.   For  example,  this  code  is
               returned when an attempt is made to split  a  sub-
               disk  on  a  striped  plex, or to use a split size
               that is greater than the size of the plex.

     (21) VEX_IOERR
               An I/O error was encountered that caused the util-
               ity to abort an operation.

     (22) VEX_NOPLEX
               A volume involved in an operation did not have any
               associated  plexes,  although  at  least  one  was
               required.

     (23) VEX_NOSUBDISK
               A plex involved in an operation did not  have  any
               associated  subdisks,  although  at  least one was
               required.

     (24) VEX_UNSTARTABLE
               A volume could not be started by the  vxvol  start
               operation, because the configuration of the volume
               and its plexes prevented the operation.

     (25) VEX_STARTED
               A specified volume was already started.

     (26) VEX_UNSTARTED
               A specified volume was not started.  For  example,
               this  code is returned by the vxvol stop operation
               if the operation is given a  volume  that  is  not
               started.

     (27) VEX_DETACHED
               A volume or plex involved in an  operation  is  in
               the  detached  state, thus preventing a successful
               operation.

     (28) VEX_DISABLED
               A volume or plex involved in an  operation  is  in
               the  disabled  state, thus preventing a successful
               operation.

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Maintenance Commands                                  vxintro(1M)

     (29) VEX_ENABLED
               A volume or plex involved in an  operation  is  in
               the  enabled  state,  thus preventing a successful
               operation.

     (30) VEX_UNKNOWN
               An unknown error was encountered.  This  code  may
               be  used,  for  example,  when  the  volume daemon
               returns an unrecognized error number.

     (31) VEX_OPEN
               An operation failed because a  volume  device  was
               open  or mounted, or because a subdisk was associ-
               ated with an open or mounted volume or plex.

     Exit codes greater than 32 are reserved  for  use  by  usage
     types.   Codes  greater  than  64 can be reserved for use by
     specific utilities.

SEE ALSO
     mount(1M),    vxassist(1M),    vxconfigd(1M),    vxdctl(1M),
     vxdg(1M),    vxdisk(1M),    vxdiskadd(1M),    vxdiskadm(1M),
     vxdisksetup(1M),  vxdmpadm(1M),   vxedit(1M),   vxencap(1M),
     vxevac(1M),     vxinfo(1M),     vxiod(1M),    vxlicense(1M),
     vxmake(1M),    vxmend(1M),    vxmirror(1M),    vxnotify(1M),
     vxplex(1M),   vxprint(1M),   vxr5check(1M),  vxreattach(1M),
     vxrecover(1M), vxrelayout(1M),  vxrelocd(1M),  vxresize(1M),
     vxrootmir(1M),   vxsd(1M),   vxsparecheck(1M),   vxstat(1M),
     vxtask(1M),    vxtrace(1M),     vxunroot(1M),     vxvol(1M),
     vxwatch(1M), plexrec(4), sdrec(4), vxrec(4), vxmake(4)

     For information about other aspects of the  Volume  Manager,
     see:

     vxintro(3X), vxio(7), vxinfo(7)

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# 

