| The Cuddletech Veritas Volume Manager Series: Volume Kreation: VxAssist & Ways to spend more time cuddling | ||
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RAID5 is pretty simple to deal with. You can get pretty specific about the volume setup using vxassist, but generally when you are using RAID5 you're not looking to break any benchmarks. Therefore there is no more to it's creation than specifying the layout as "raid5", and specifying any disks you want to use. The syntax again is:
vxassist -g <diskgroup> -U <usagetype> make <volname> <size> \ layout=<layouttype> <disk1> <disk2> <disk3> ... |
RAID5 does have some requirements, though, you must use at least 3 vmdisk (4 is preferable) to create a RAID5 volumes, of which 3 subdisks are used for the volume itself, and 1 subdisk is automatically created as a RAID5 log plex. A RAID5 log is used for volume metadata and parity logging. While you do not absolutely need a RAID5, you would be a fool to not use one, and vxassist just assumes give you on right away.
Let's look at an example of a RAID5 volumes building built:
# vxassist -g cuddledg -U fsgen make raid5vol 4g layout=raid5 # vxprint -g cuddledg -hrt raid5vol V NAME USETYPE KSTATE STATE LENGTH READPOL PREFPLEX PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE SD NAME PLEX DISK DISKOFFS LENGTH [COL/]OFF DEVICE MODE SV NAME PLEX VOLNAME NVOLLAYR LENGTH [COL/]OFF AM/NM MODE dm cuddle-f0 c1t0d0s2 sliced 3590 17678493 - dm cuddle-f1 c1t1d0s2 sliced 3590 17678493 - dm cuddle-f2 c1t2d0s2 sliced 3590 17678493 - dm cuddle-f3 c1t3d0s2 sliced 3590 17678493 - dm cuddle-f4 c1t4d0s2 sliced 3590 17678493 - dm cuddle-f5 c1t5d0s2 sliced 3590 17678493 - dm cuddle-f6 c1t6d0s2 sliced 3590 17678493 - v raid5vol raid5 ENABLED ACTIVE 8388640 RAID - pl raid5vol-01 raid5vol ENABLED ACTIVE 8402880 RAID 6/32 RW sd cuddle-f0-01 raid5vol-01 cuddle-f0 0 1680588 0/0 c1t0d0 ENA sd cuddle-f1-01 raid5vol-01 cuddle-f1 0 1680588 1/0 c1t1d0 ENA sd cuddle-f2-01 raid5vol-01 cuddle-f2 0 1680588 2/0 c1t2d0 ENA sd cuddle-f3-01 raid5vol-01 cuddle-f3 0 1680588 3/0 c1t3d0 ENA sd cuddle-f4-01 raid5vol-01 cuddle-f4 0 1680588 4/0 c1t4d0 ENA sd cuddle-f5-01 raid5vol-01 cuddle-f5 0 1680588 5/0 c1t5d0 ENA pl raid5vol-02 raid5vol ENABLED LOG 3591 CONCAT - RW sd cuddle-f6-01 raid5vol-02 cuddle-f6 0 3591 0 c1t6d0 ENA # |
Here we see that vxassist descided to work with 6 disks for the actual volume, and then created a very small (1.5M) subdisk for a RAID5 log plex. We could alternately have specified the number of columns we wanted in the RAID5 volumes using the option "ncolumns", just like we did to control striped volumes in the previous examples. But remember, if you specify "ncolumns" as 5, and you want to specify disks to use, to specify 6 disks for use so that you don't end up forcing vxassist to put the log plex on one of the data disks.
Here's one more RAID5 example with alittle more clarify than before:
# vxassist -g cuddledg -U fsgen make raid5vol 4g layout=raid5 ncolumns=3 cuddle-f0 cuddle-f1 cuddle-f2 cuddle-f3 # vxprint -g cuddledg -hrt raid5vol V NAME USETYPE KSTATE STATE LENGTH READPOL PREFPLEX PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE SD NAME PLEX DISK DISKOFFS LENGTH [COL/]OFF DEVICE MODE SV NAME PLEX VOLNAME NVOLLAYR LENGTH [COL/]OFF AM/NM MODE dm cuddle-f0 c1t0d0s2 sliced 3590 17678493 - dm cuddle-f1 c1t1d0s2 sliced 3590 17678493 - dm cuddle-f2 c1t2d0s2 sliced 3590 17678493 - dm cuddle-f3 c1t3d0s2 sliced 3590 17678493 - v raid5vol raid5 ENABLED ACTIVE 8388608 RAID - pl raid5vol-01 raid5vol ENABLED ACTIVE 8395712 RAID 3/32 RW sd cuddle-f0-01 raid5vol-01 cuddle-f0 0 4197879 0/0 c1t0d0 ENA sd cuddle-f1-01 raid5vol-01 cuddle-f1 0 4197879 1/0 c1t1d0 ENA sd cuddle-f2-01 raid5vol-01 cuddle-f2 0 4197879 2/0 c1t2d0 ENA pl raid5vol-02 raid5vol ENABLED LOG 3591 CONCAT - RW sd cuddle-f3-01 raid5vol-02 cuddle-f3 0 3591 0 c1t3d0 ENA # |
Wham, just what I asked for, ready to go. It's VxVM awsome!