For many a year, SDDPCM ruled the world of IBM SAN attached storage on AIX servers. For example, with IBM SVC disk.

 

 Times are changing.

 

The recommended multi-path driver to use on IBM AIX and VIOS when attached to SVC and Storwize storage devices running microcode levels V7.6.1 and later is changing from the SDDPCM to the default AIX PCM. Please read the following technote on the subject.

 

https://www-01.ibm.com/support/docview.wss?uid=ssg1S1010218

 

In addition to the removal of support for the SVC, support for the DS8000 (2107DS8K) storage devices is also being retired and customers are encouraged to migrate away from SDDPCM.

 

SDDPCM is not supported on POWER9 servers.  

 

The official way to migrate from SDDPCM to AIXPCM is documented here (please read this):

 

How To Migrate SDDPCM to AIXPCM

http://www-01.ibm.com/support/docview.wss?uid=ssg1S1010646

 

Here’s another way.

 

Use the manage_disk_drivers command.

 

https://www.ibm.com/support/knowledgecenter/sv/ssw_aix_72/com.ibm.aix.cmds3/manage_disk_drivers.htm

 

This command allows administrators to choose between different Patch Control Modules (PCMs), or between using a PCM and configuring the disks as non-MPIO disks.

 

It may be the easiest method for transitioning from using SDDPCM to the AIX default PCM.

 

The -l option shows a list of all options available (the columns show the device family, the driver currently used by that family, and the different options available).

 

# manage_disk_drivers -l | grep -i svc

IBMSVC              NO_OVERRIDE           NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO

 

The "NO_OVERRIDE" option indicates that the configuration is not overridden by manage_disk_drivers, and so the device family is configured based on the available ODM to match that family. The ODM supplied by SDDPCM takes precedence over the AIX default PCM ODM.  So a value of "NO_OVERRIDE" indicates that SDDPCM is used to configure devices of that family if SDDPCM is installed.  If SDDPCM is not installed, then the AIX default PCM is used.

 

By selecting the "AIX_AAPCM" option, the administrator can instruct AIX to use the AIX default PCM even if SDDPCM is installed. The AIX LPAR must be rebooted in order for the disks to be reconfigured to use the AIX PCM.  Once AIX is rebooted, SDDPCM is no longer in use for the disk family specified in the manage_disk_drivers command.  If no disks are using SDDPCM, then the SDDPCM filesets may be uninstalled.




Note: The values of the attributes of the disks are not preserved during this conversion.  In particular, the AIX default PCM uses the "single_path" reservation policy as the default reservation policy, and the "fail_over" algorithm as the default algorithm. If the disks being switched from SDDPCM to AIX PCM are shared among multiple nodes in a cluster, this default reservation policy must be changed before the disk is opened.  If this is not done, other nodes in the cluster will lose access to the shared disks until the reservation policy is changed. The chdev command may be used to change the reservation policy. This also applies to VSCSI backing disks in a dual VIOS environment. In my opinion it is a good idea to add the recommended values to the predefined attributes in ODM. These values should be applied BEFORE rebooting your system into AIXPCM mode.

# 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

Any future LUN will now have the recommended values.

 

I personally recommend (and this is not an official IBM recommendation), to use the following defaults for AIX PCM hdisks.

 

# chdev -l hdiskX -a algorithm=shortest_queue -a reserve_policy=no_reserve –a queue_depth=32 -a hcheck_interval=60 -U

 

Here’s an example of using the manage_disk_drivers  command to switch from SDDPCM to AIX PCM for a system that’s using IBM SVC 2145 disk.

 

a) Confirm the system is using SDDPCM for MPIO.

 

# manage_disk_drivers -l | grep -i svc

IBMSVC              NO_OVERRIDE           NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO

 

# pcmpath query device

 

Total Dual Active and Active/Asymmetric Devices : 2

 

 

DEV#:   3  DEVICE NAME: hdisk2  TYPE: 2145  ALGORITHM:  Load Balance

SERIAL: 60050768017F00362000000000000346  VENDOR: IBM  SIZE: 30.00 GB

 

==========================================================================

Path#      Adapter/Path Name          State     Mode     Select     Errors

    0*          fscsi0/path0           OPEN   NORMAL         50          0

    1           fscsi0/path1           OPEN   NORMAL       9343          0

    2*          fscsi1/path2           OPEN   NORMAL         51          0

    3           fscsi1/path3           OPEN   NORMAL       9236          0

 

DEV#:   4  DEVICE NAME: hdisk3  TYPE: 2145  ALGORITHM:  Load Balance

SERIAL: 60050768017F00362000000000000347  VENDOR: IBM  SIZE: 2.00 TB

 

==========================================================================

Path#      Adapter/Path Name          State     Mode     Select     Errors

    0           fscsi0/path0           OPEN   NORMAL        117          0

    1*          fscsi0/path1           OPEN   NORMAL         36          0

    2           fscsi1/path2           OPEN   NORMAL        121          0

    3*          fscsi1/path3           OPEN   NORMAL         36          0

 

The AIX PCM lsmpio command does not return anything, as SDDPCM is in control at this time.

 

# lsmpio -are

#

 

# lsdev -Cc disk

hdisk2 Available 42-T1-01 MPIO FC 2145

hdisk3 Available 42-T1-01 MPIO FC 2145

# lspath

Enabled hdisk2 fscsi0

Enabled hdisk3 fscsi0

Enabled hdisk2 fscsi0

Enabled hdisk3 fscsi0

Enabled hdisk2 fscsi1

Enabled hdisk3 fscsi1

Enabled hdisk2 fscsi1

Enabled hdisk3 fscsi1

 

b) Run the manage_disk_drivers command to switch to AIX PCM and reboot the system.

 

# manage_disk_drivers -d IBMSVC -o AIX_AAPCM

 ********************** ATTENTION *************************

  For the change to take effect the system must be rebooted

 

# bosboot -ad /dev/ipldevice

# shutdown –Fr

 

After the reboot, AIX PCM is now in control of MPIO on this system.

 

# manage_disk_drivers -l | grep -i svc

IBMSVC              AIX_AAPCM             NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO

 

# lsmpio -are

Adapter Driver: fscsi0 -> AIX PCM

    Adapter WWPN:  c0507607e05e0078

    Link State:    Up

    Connection Errors

    Last 10 Minutes:                          0

    Last 60 Minutes:                          0

    Last 24 Hours:                            0

    Total Errors:                             0

 

                               Connection Errors

                            Last 10         Last 60         Last 24

                            Minutes         Minutes         Hours

    50050768011006c4              0               0               0

    500507680110062b              0               0               0

 

Adapter Driver: fscsi1 -> AIX PCM

    Adapter WWPN:  c0507607e05e007a

    Link State:    Up

    Connection Errors

    Last 10 Minutes:                          0

    Last 60 Minutes:                          0

    Last 24 Hours:                            0

    Total Errors:                             0

 

                               Connection Errors

                            Last 10         Last 60         Last 24

                            Minutes         Minutes         Hours

    50050768011006c4              0               0               0

    500507680110062b              0               0               0

 

s82861p22:/ #

 

# pcmpath query device

No device file found

What if I wanted to roll back to SDDPCM? Simple, just run manage_disk_drivers again and select NO_OVERRIDE. Of course, this assumes you have not de-installed the SDDPCM device drivers.

 

# manage_disk_drivers -d IBMSVC -o NO_OVERRIDE

 ********************** ATTENTION *************************

  For the change to take effect the system must be rebooted

# shutdown -Fr

 

SDDPCM is now in control of MPIO again.

 

# manage_disk_drivers -l | grep -i svc

IBMSVC              NO_OVERRIDE           NO_OVERRIDE,AIX_AAPCM,AIX_non_MPIO

 

# pcmpath query device

 

Total Dual Active and Active/Asymmetric Devices : 2

 

DEV#:   3  DEVICE NAME: hdisk2  TYPE: 2145  ALGORITHM:  Load Balance

SERIAL: 60050768017F00362000000000000346  VENDOR: IBM  SIZE: 30.00 GB

 

==========================================================================

Path#      Adapter/Path Name          State     Mode     Select     Errors

    0*          fscsi0/path0           OPEN   NORMAL         50          0

    1           fscsi0/path1           OPEN   NORMAL       9637          0

    2*          fscsi1/path2           OPEN   NORMAL         51          0

    3           fscsi1/path3           OPEN   NORMAL       9674          0

 

DEV#:   4  DEVICE NAME: hdisk3  TYPE: 2145  ALGORITHM:  Load Balance

SERIAL: 60050768017F00362000000000000347  VENDOR: IBM  SIZE: 2.00 TB

 

==========================================================================

Path#      Adapter/Path Name          State     Mode     Select     Errors

    0           fscsi0/path0           OPEN   NORMAL        144          0

    1*          fscsi0/path1           OPEN   NORMAL         36          0

    2           fscsi1/path2           OPEN   NORMAL        109          0

    3*          fscsi1/path3           OPEN   NORMAL         36          0

 

AIX PCM lsmpio does not return any information when SDDPCM is in control.

 

# lsmpio

#

 

Now, when you’ve switched from SDDPCM to AIX PCM, you can uninstall the SDDPCM device drivers at this point.

 

; Confirm AIX PCM is in control i.e. output from lsmpio.

 

# lsmpio

  name    path_id  status   path_status  parent  connection

 

  hdisk2  0        Enabled  Non          fscsi0  50050768011006c4,0

  hdisk2  1        Enabled  Opt          fscsi0  500507680110062b,0

  hdisk2  2        Enabled  Non          fscsi1  50050768011006c4,0

  hdisk2  3        Enabled  Sel,Opt      fscsi1  500507680110062b,0

  hdisk3  0        Enabled  Opt          fscsi0  50050768011006c4,1000000000000

  hdisk3  1        Enabled  Non          fscsi0  500507680110062b,1000000000000

  hdisk3  2        Enabled  Sel,Opt      fscsi1  50050768011006c4,1000000000000

  hdisk3  3        Enabled  Non          fscsi1  500507680110062b,1000000000000

 

 

# smit deinstall

 

                              Remove Installed Software

 

Type or select values in entry fields.

Press Enter AFTER making all desired changes.

 

                                                        [Entry Fields]

* SOFTWARE name   [devices.fcp.disk.ibm.mpio.rte devices.sddpcm.72.rte]                                                                     

  PREVIEW only? (remove operation will NOT occur)     yes      +

  REMOVE dependent software?                          yes      +

  EXTEND file systems if space needed?                no       +

  DETAILED output?                                             +

 

 

  FILESET STATISTICS

  ------------------

      2  Selected to be deinstalled, of which:

          2  Passed pre-deinstall verification

    ----

      2  Total to be deinstalled

 

  ADDITIONAL INFORMATION

  ----------------------

  One or more of the selected filesets will cause a bosboot to be performed.

  The bosboot command will rebuild the boot image.  As a result it may

  be necessary to reboot your system for the changes to take effect.

 

  It is recommended that you reboot the system as soon as possible

  after the installation of this software to avoid disruption of

  current functionality.

 

  Name                        Level           Part        Event       Result

  -------------------------------------------------------------------------------

  devices.sddpcm.72.rte       2.7.1.0         ROOT        DEINSTALL   SUCCESS

  devices.sddpcm.72.rte       2.7.1.0         USR         DEINSTALL   SUCCESS

  devices.fcp.disk.ibm.mpio.r 1.0.0.25        USR         DEINSTALL   SUCCESS

    

# lslpp -l | grep sddpcm

#

# pcmpath query device

ksh: pcmpath:  not found.

 

Note: Please take note of the following important information in the Technote (S1010218) I mentioned earlier:

 

“Note1: Removing SDDPCM will set the queue to the default value of 20. Any modification made to the queue depth prior to removal will need to be reapplied.

Note2: The default path selection algorithm for AIXPCM is "fail_over". The AIX PCM supports the "shortest_queue" algorithm which is similar to SDD PCM's "load_balance" algorithm. The chdev command may be used to set the algorithm, though it may also be necessary to set the reserve policy when changing the algorithm. For example, to set hdisk5 to use the "shortest_queue" algorithm, execute this command: chdev -l hdisk5 -a algorithm=shortest_queue -a reserve_policy=no_reserve

Note3: Multipath management commands differ between AIXPCM and SDDPCM. If the SDDPCM is removed from your system any scripts that have been generated that utilize these commands will need to be modified to use the corresponding AIXPCM commands.”

 

Tags:  blog chris mpio gibson sddpcm pcm aix