Migrating from SDDPCM to AIXPCM (the easy way)
For a while now, IBM have diverted their efforts in storage multipathing from SDDPCM to the default AIX PCM [1]. This brings a few advantages, but specifically for me, it means the driver is now updated as part of the AIX system maintenance, and is no longer something I need to maintain separately. All significant functionality that SDDPCM provides, can now be provided by the default AIX PCM driver.
For those currently using SDDPCM, removing the driver can be somewhat complicated, and even more so when the boot LUN (rootvg LUN) is being managed by SDDPCM. Buried deep in the Multipath Subsystem Device Driver User’s Guide is a command called manage_disk_drivers. The manage_disk_drivers command can be used to display a list of storage families, and the driver that manages or supports each family. This allows us to easily (with a reboot if you boot from an SDDPCM managed device) switch the driver from SDDPCM to AIXPCM (or vice versa).
Below I detail how to switch from SDDPCM to AIXPCM when using LUN’s presented to the host via SVC.
Existing driver manging IBMSVC.
From the man page for manage_disk_drivers
If the present driver attribute is set to NO_OVERRIDE, the AIX operating system selects an alternate path control module (PCM), such as Subsystem Device Driver Path Control Module (SDDPCM), if it is installed.
# manage_disk_drivers -l Device Present Driver Driver Options 2810XIV AIX_AAPCM AIX_AAPCM,AIX_non_MPIO DS4100 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4200 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4300 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4500 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4700 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4800 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS3950 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS5020 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DCS3700 AIX_APPCM AIX_APPCM DCS3860 AIX_APPCM AIX_APPCM DS5100/DS5300 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS3500 AIX_APPCM AIX_APPCM XIVCTRL MPIO_XIVCTRL MPIO_XIVCTRL,nonMPIO_XIVCTRL 2107DS8K NO_OVERRIDE NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO IBMFlash NO_OVERRIDE NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO IBMSVC NO_OVERRIDE NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO
Switch to using AIXPCM (and reboot).
# manage_disk_drivers -d IBMSVC -o AIX_AAPCM ********************** ATTENTION ************************* For the change to take effect the system must be rebooted
After reboot, you will now see AIX_AAPCM as the present driver being used.
# manage_disk_drivers -l Device Present Driver Driver Options 2810XIV AIX_AAPCM AIX_AAPCM,AIX_non_MPIO DS4100 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4200 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4300 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4500 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4700 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS4800 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS3950 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS5020 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DCS3700 AIX_APPCM AIX_APPCM DCS3860 AIX_APPCM AIX_APPCM DS5100/DS5300 AIX_SDDAPPCM AIX_APPCM,AIX_SDDAPPCM DS3500 AIX_APPCM AIX_APPCM XIVCTRL MPIO_XIVCTRL MPIO_XIVCTRL,nonMPIO_XIVCTRL 2107DS8K NO_OVERRIDE NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO IBMFlash NO_OVERRIDE NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO IBMSVC AIX_AAPCM NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO
From here, you can do one of two things. Leave the SDDPCM driver installed, as this will allow for easy rollback should you experience performance issues, or other driver related problems. Or completely remove the SDDPCM driver from the LPAR.
A few things to keep in mind.
- If you’ve modified the queue_depth attribute on the hdisk, this will be reset to the AIXPCM default of 20. There is already a good write up on best practises and considerations when working with the default AIXPCM driver [2].
- When using SDDPCM, you would have used the pcmpath command to display and manage devices. As above, someone has already written a good write up on resiliency and problem determination, and some common lsmpio commands you’ll want to know [3]
Taking the IBM recommendations into account, I’ll set the hdisk attributes accordingly.
# lsdev -Cc disk -F name | while read line; do chdev -l ${line} -a queue_depth=32 -a reserve_policy=no_reserve -a algorithm=shortest_queue -P; done
hdisk0 changed
hdisk1 changed
Another handy command, which isn’t related to the overall driver migration, is using chdef to change the default values of the predefined attributes in ODM. Any future LUN’s presented to the host will now have the queue_depth, reserve_policy, and algorithm set to the values I want.
# chdef -a queue_depth=32 -c disk -s fcp -t mpioosdisk queue_depth changed # chdef -a reserve_policy=no_reserve -c disk -s fcp -t mpioosdisk reserve_policy changed # chdef -a algorithm=shortest_queue -c disk -s fcp -t mpioosdisk algorithm changed
Rollback
Should you need to go back to using SDDPCM as the driver, and haven’t removed it, you can use manage_disk_drivers to flip back and reboot.
# manage_disk_drivers -d IBMSVC -o NO_OVERRIDE ********************** ATTENTION ************************* For the change to take effect the system must be rebooted
[1] – https://www-01.ibm.com/support/docview.wss?uid=ssg1S1010218
[2] – https://www.ibm.com/developerworks/aix/library/au-aix-mpio/index.html
[3] – https://www.ibm.com/developerworks/aix/library/au-aix-multipath-io-mpio/index.html
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