Migrating a SAN root disk from IBM Multipath I/O (MPIO) to Dynamic Multi-Pathing (DMP)

Problem

IBM MPIO is automatically enabled on AIX on all capable devices, and DMP and other third-party multi-pathing software cannot manage the paths to these disks/LUNs. In some cases, MPIO manages the devices using a plug-in called path control module (PCM) which is provided by the storage vendor. IBM MPIO or MPIO PCM works on the granularity of the storage model, so if there are non-root LVMs present on the same storage, they should also be migrated to DMP.

Solution

Migrating to DMP from MPIO or MPIO PCM

This procedure describes how to migrate to DMP from MPIO or an MPIO PCM. The procedure includes removing the devices from MPIO control and enabling DMP on the devices. If an MPIO PCM is installed, you need to remove the PCM before you install the ODM packages from the vendor.
Note: Plan for system downtime for the following procedure.

The migration steps involve system downtime because: 

• Host needs to stop applications
• Host needs to stop the VCS services, if using VCS
• The procedure involves one or more host reboots

To take the devices out of MPIO control and enable DMP:

1. Obtain the corresponding MPIO-suppression ODM fileset for the array from the array vendor. If the MPIO suppression ODM fileset is not available, use the vxmpio utility to remove the device from MPIO. 
2. Stop the applications that use the MPIO devices. 
3. Unmount the file systems on the MPIO devices. 
4. Vary off the LVM volume groups:
   # varyoffvg vgroupname
5. If an MPIO PCM is installed, remove all Veritas Volume Manager (VxVM) devices that the PCM controls:
   # vxdisk rm dmpnodename
6. If the MPIO PCM does not control the rootvg devices, then uninstall the PCM.
   If a PCM controls the rootvg devices, then you must obtain the script from the PCM vendor to uninstall the PCM. For example, if the Subsystem Device Driver Path Control Module (SDDPCM) controls the devices, then contact IBM to obtain the script to remove SDDPCM.
7. Install the MPIO-suppression ODM fileset that you obtained from the array vendor in step 1. Refer to the array vendor documentation for the installation procedure.
   Some array vendors do not distribute ODM pre-defines for their arrays for AIX. In this case, you can use the devices as hdisk devices, as long as MPIO does not claim these LUNs.
8. If there are non-root LVMs on the same storage, they should also be migrated to DMP using the following command. Even if you plan to create non-root LVMs in the future, you should use the following command:
   # vxdmpadm settune dmp_native_support=on
   
   If there are no non-root LVMs currently present and if there is no plan to create on the same storage in future, you can use the following command to enable DMP support for root LVM only:
   # vxdmpadm native enable vgname=rootvg
9. Reboot the system. 
10. After the reboot, DMP controls the devices. 
11. Mount the file systems. 
12. Restart the applications.
     

Migrating to DMP using the vxmpio utility

Some devices do not have vendor supplied non-MPIO ODM definitions to disable MPIO. In this case, you can use the vxmpio utility for removing the MPIO definitions for those devices.

The vxmpio utility controls whether the specified type of storage array is controlled by MPIO or is claimed under the DMP driver. Use the vxmpio utility to disable or enable MPIO for devices with the specified product ID (PID). You must reboot the system for the changes to take effect. When you disable MPIO, the specified devices are claimed under the DMP driver after the reboot. When you enable MPIO, the specified devices are removed from DMP control and claimed under MPIO.

For more information about the vxmpio utility, refer to the vxmpio (1M) manual page.

The following procedure describes how to disable MPIO using the vxmpio utility. In this procedure, as an example, hdisk9 residing on SAN-VC is modified.

To disable MPIO using the vxmpio utility:

1. Check the available disks:
   # vxdisk -e list
   DEVICE       TYPE           DISK         GROUP        STATUS        OS_NATIVE_NAME   ATTR
   disk_0       auto           -             -            LVM          hdisk0           -
   disk_1       auto           -             -            LVM          hdisk1           - 
   ...
   san_vc0_9    auto:cdsdisk   -             -            online       hdisk9           -
    
2. Verify if the disk is under MPIO control at the operating system (OS) level:
   # lscfg -vl hdisk9
   hdisk9 U9179.MHD.06B94ER-V86-C5-T1-W500507680140C156-L0 MPIO IBM 2145 FC Disk
   Manufacturer................IBM
   Machine Type and Model......2145
   ROS Level and ID............30303030
   Serial Number...............2145
   Device Specific.(Z0)........0000063268181002
   Device Specific.(Z1)........
   Device Specific.(Z2)........
   Device Specific.(Z3)........
   
   Note: MPIO is included in the description above. To turn off MPIO for disks on the SAN-VC, the disks have to be identified by the PID of the storage array. In this case, SAN-VC storage has the identifier "2145".
    
3. Turn off MPIO control of disks on the SAN (reboot may be required):
   # /etc/vx/bin/vxmpio disable pid='2145'
   Running bosboot ..
   trustchk: Verification of attributes failed: /usr/sbin/mknod: mode
   bosboot: Boot image is 61468 512 byte blocks.
   VxVM vxmpio INFO V-5-2-5828 Please reboot the machine to disable MPIO support for 2145
   # shutdown -Fr now
    
4. After reboot, verify whether MPIO has been disabled for this storage. After reboot, the command for the disk at OS level should no longer show MPIO in the description output.
   # lscfg -vl hdisk9
   hdisk9 U9179.MHD.06B94ER-V86-C5-T1-W500507680140C156-L0 IBM 2145 FC Disk