Source:
Many AIX systems still use SDDPCM as a multipathing solution. However, SDDPCM is no longer supported on POWER 9 hardware from IBM.
The following is the migration from SDDPCM to AIX PCM. On our example system we have the following physical volumes:
$ lspv
hdisk0 00abcdefabcde000 datavg active
hdisk1 00abcdefabcde001 datavg active
hdisk2 none None
hdisk3 00abcdefabcde003 altinst_rootvg
hdisk4 00abcdefabcde004 rootvg active
$The Physical Volumes are disks that are made available through an SVC:
$ lsdev -l hdisk0 -F uniquetype
disk/fcp/2145
$The Path Control Module (PCM) uses SDDPCM:
$ lsattr -El hdisk0 -a PCM -F value
PCM/friend/sddpcm
$You can also see this when looking at the list of kernel extensions:
$ genkex | grep pcm
f1000000c012a000 af000 /usr/lib/drivers/sddpcmke
$Which PCM driver is used for which disk types can be easily viewd with the command “manage_disk_drivers”:
$ 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 AIX_AAPCM,AIX_non_MPIO,NO_OVERRIDE
IBMFlash NO_OVERRIDE AIX_AAPCM,AIX_non_MPIO,NO_OVERRIDE
IBMSVC NO_OVERRIDE AIX_AAPCM,AIX_non_MPIO,NO_OVERRIDE
$In our case, SVC disks, the last line is relevant (IBMSVC). As current PCM driver NO_OVERRIDE is listed here, possible other drivers are AIX_AAPCM (AIX PCM for active / active and ALUASystems) and AIX_non_MPIO (drives without multi-pathing). The value NO_OVERRIDE means that if no multipathing driver is explicitly specified, a multipathing driver is used if possible (if available), otherwise no multipathing driver is used. If more than one multipathing driver is available (in our case AIX PCM and SDDPCM, then SDDPCM has priority).
In a subsequent blog entry, we will take a closer look at the possible values, as well as the point in AIX where the selection is made.
Before we change the driver for IBMSVC disks (a reboot is necessary), let’s take a look at the attributes of our disks, here an example for the hdisk0:
$ lsattr -El hdisk0
PCM PCM/friend/sddpcm PCM True
...
algorithm load_balance Algorithm True+
...
queue_depth 120 Queue DEPTH True+
...
reserve_policy no_reserve Reserve Policy True+
...
$Changing the driver will cause the values of some set attributes to be lost or replaced by new default values of the new driver. This is especially true for the queue_depth (here: 120), the reserve_policy (here: no_reserve) and the load-balancing policy (algorithm). The current values should be noted, then after the conversion to the AIX PCM driver then adjust accordingly.
Switching to AIX PCM can be done with the command “manage_disk_drivers”. For this, the command is given the disk type (here IBMSVC) with the option “-d” and the desired driver (here AIX_AAPCM for the AIX PCM driver) with the option “-o”:
# manage_disk_drivers -d IBMSVC -o AIX_AAPCM
********************** ATTENTION *************************
For the change to take effect the system must be rebooted
#The changed configuration can be listed directly with “manage_disk_drivers -l”:
$ manage_disk_drivers -l
Device Present Driver Driver Options
...
IBMSVC AIX_AAPCM AIX_AAPCM,AIX_non_MPIO,NO_OVERRIDE
$To make the change, the system must now be rebooted:
# shutdown -r now
SHUTDOWN PROGRAM
Thu Feb 7 09:43:38 CET 2019
...We execute the 3 commands from the beginning again (lspv, lsdevund lsattr):
$ lspv
hdisk0 00abcdefabcde000 datavg active
hdisk1 00abcdefabcde001 datavg active
hdisk2 none None
hdisk3 00abcdefabcde003 altinst_rootvg
hdisk4 00abcdefabcde004 rootvg active
$The physical volumes are unchanged.
$ lsdev -l hdisk0 -F uniquetype
disk/fcp/mpioosdisk
$The type of disks has changed from disk / fcp / 2145 to disk / fcp / mpioosdisk. This already indicates that the multipathing driver has changed.
$ lsattr -El hdisk0 -a PCM -F value
PCM/friend/fcpother
$The Path Control Module (PCM) has also changed. The guy is no longer sddpcm but fcpother. That does not look directly after AIX PCM. However, a look at the corresponding driver shows immediately that AIX PCM is in use here:
$ lsdev -P -c PCM -s friend -t fcpother -F DvDr
aixdiskpcmke
$The associated kernel extension aixdiskpcmke is also currently loaded and in use:
$ genkex | grep pcm
73e2000 57000 /usr/lib/drivers/aixdiskpcmke
$Let’s take a look at the attributes of hdisk0 again. We expect changed values for some attributes here:
$ lsattr -El hdisk0
PCM PCM/friend/fcpother Path Control Module False
...
algorithm fail_over Algorithm True+
...
queue_depth 20 Queue DEPTH True+
...
reserve_policy single_path Reserve Policy True+
...
$The value 120 for the queue_depth has been lost and has been replaced by the default value 20. The reserve_policy has changed to single_path and the load-balancing algorithm is now fail_over, i. only one path is used at a time.
We change the settings to a configuration that corresponds to the initial situation:
# chdev -P -l hdisk0 -a queue_depth=128 -a max_transfer=0x100000 -a algorithm=shortest_queue -a reserve_policy=no_reserve
hdisk0 changed
#Since the Physical Volume is in use, the setting can only be changed in the ODM and a further reboot is necessary.
After all disks have been reconfigured via the ODM, the system must be rebooted a second time:
# shutdown -r now
SHUTDOWN PROGRAM
Thu Feb 6 20:07:12 CET 2019
...After the reboot SDDPCM can be uninstalled:
# installp -u devices.fcp.disk.ibm.mpio.rte devices.sddpcm.72.rte
+-----------------------------------------------------------------------------+
Pre-deinstall Verification...
+-----------------------------------------------------------------------------+
Verifying selections...done
Verifying requisites...done
Results...
SUCCESSES
...
0503-292 This update will not fully take effect until after a
system reboot.
* * * A T T E N T I O N * * *
System boot image has been updated. You should reboot the
system as soon as possible to properly integrate the changes
and to avoid disruption of current functionality.
installp: bosboot process completed.
+-----------------------------------------------------------------------------+
Summaries:
+-----------------------------------------------------------------------------+
Installation Summary
--------------------
Name Level Part Event Result
-------------------------------------------------------------------------------
devices.sddpcm.72.rte 2.7.1.1 ROOT DEINSTALL SUCCESS
devices.sddpcm.72.rte 2.7.1.1 USR DEINSTALL SUCCESS
devices.fcp.disk.ibm.mpio.r 1.0.0.25 USR DEINSTALL SUCCESS
#The SDDPCM fileset, as well as the associated host-attachment fileset, were successfully uninstalled.
Since the SDDPCM driver was not loaded, and thus no changes have been made to the kernel, actually another reboot should not be necessary. However, since it is explicitly pointed out a quick reboot, and it is also a good idea to do a reboot test with the final configuration, we reboot the system a third and final time:
# shutdown -r now
SHUTDOWN PROGRAM
Thu Feb 6 20:17:21 CET 2019
...After the reboot, we check the disk attributes again:
$ lsattr -El hdisk0
PCM PCM/friend/fcpother Path Control Module False
...
algorithm shortest_queue Algorithm True+
...
queue_depth 120 Queue DEPTH True+
...
reserve_policy no_reserve Reserve Policy True+
...
$The system now uses the AIX PCM driver for multipathing:
$ manage_disk_drivers -l
Device Present Driver Driver Options
...
IBMSVC AIX_AAPCM AIX_AAPCM,AIX_non_MPIO,NO_OVERRIDE
$Migrating from SDDPCM to AIX PCM is pretty easy to do.
