Enabling and Disabling I/O paths with Veritas
Veritas Volume Manager (VxVM) comes with DMP (Dynamic MultiPathing) support. DMP allows VxVM to load-balance IOs across multiple controllers, offline paths when failures are detected, and dynamically disable paths when performing maintenance on a specific controller or path (e.g., ugprading a SAN switch or hot swapping an HBA). The process of manually disabling a path is easily accomplished by invoking VxVM’s vxdmpadm(1m) utility with the “disable” keyword, and the controller to disable:
$ vxdmpadm disable ctlr=c2
Once the controller is disabled you can monitor the number of IOs per path with vxdmpadm(1m)’s iostat utility:
$ vxdmpadm iostat show dmpnodename=c2t20d1s2 interval=5
cpu usage = 636us per cpu memory = 32768b
OPERATIONS KBYTES AVG TIME(ms)
PATHNAME READS WRITES READS WRITES READS WRITES
c2t20d1s2 1800 0 230400 0 0.016102 0.000000
c3t21d1s2 1799 0 230272 0 0.016858 0.000000
cpu usage = 663us per cpu memory = 32768b
OPERATIONS KBYTES AVG TIME(ms)
PATHNAME READS WRITES READS WRITES READS WRITES
c2t20d1s2 337 0 43136 0 0.014257 0.000000
c3t21d1s2 3007 0 384896 0 0.018631 0.000000
cpu usage = 657us per cpu memory = 32768b
OPERATIONS KBYTES AVG TIME(ms)
PATHNAME READS WRITES READS WRITES READS WRITES
c2t20d1s2 0 0 0 0 0.000000 0.000000
c3t21d1s2 3357 0 429696 0 0.018183 0.000000
Once maintenance is performed, the controller can be brought back online with vxdmpadm(1m)’s “enable” option, and the controller to enable:
$ vxdmpadm enable ctlr=c2
Once the controller is back up and operational, VxVM will start sending IOs through the controller:
cpu usage = 904us per cpu memory = 32768b
OPERATIONS KBYTES AVG TIME(ms)
PATHNAME READS WRITES READS WRITES READS WRITES
c2t20d1s2 0 0 0 0 0.000000 0.000000
c3t21d1s2 4064 0 520192 0 0.014160 0.000000
cpu usage = 719us per cpu memory = 32768b
OPERATIONS KBYTES AVG TIME(ms)
PATHNAME READS WRITES READS WRITES READS WRITES
c2t20d1s2 1454 0 186112 0 0.013288 0.000000
c3t21d1s2 2720 1 348160 8 0.013732 0.250000
cpu usage = 697us per cpu memory = 32768b
OPERATIONS KBYTES AVG TIME(ms)
PATHNAME READS WRITES READS WRITES READS WRITES
c2t20d1s2 2110 0 270080 0 0.013485 0.000000
c3t21d1s2 2112 0 270336 0 0.013361 0.000000
VxVM is awesome, and makes managing tons of storage a breeze!
