6. Dynamic Multi Pathing (aka: DMP)

Dynamic Multi Pathing is used to increase disk availability. This is available when using disk arrays that allow for connection to multiple controllers. DMP does two big things for us. Firstly, it gives us multiple "paths" or physical connections to each disk in an array, so if one path fails (like if a controller, cable, GBIC, I/O board, etc. dies) the disk is still accessible. Secondly, because there are multiple I/O paths to DMP disks it allows for load balancing by splitting I/O across each path, in turn lowering load on system controllers, busses, etc. DMP can be manipulated by using the tool "vxdmpadm". This tool allows DMP to be enabled, disabled, and for various DMP operations such as disabling paths for maintenance. To see what paths are available to a given disk use the vxdisk command. (syntax: vxdisk list <devname>) DMP nice in the fact that it rarely requires administrator intervention. Quite simply, if your system is setup correctly it "just works". For further information, see the Veritas Getting Started Guide, and the vxdiskadm(1m) man page.