Sunday, August 1, 2010

EMC Powerpath and MPIO in a same box

You can run into an issue with EMC storage on AIX systems using MPIO (No Powerpath) for your boot disks:

After installing the ODM_DEFINITONS of EMC Symmetrix on your client system, the system won’t boot any more and will hang with LED 554 (unable to find boot disk).

The boot hang (LED 554) is not caused by the EMC ODM package itself, but by the boot process not detecting a path to the boot disk if the first MPIO path does not corresponding to the fscsiX driver instance where all hdisks are configured. Let me explain that more in detail:

Let’s say we have an AIX system with four HBAs configured in the following order:

# lscfg -v | grep fcs

fcs2 (wwn 71ca) -> no devices configured behind this fscsi2 driver
instance (path only configured in CuPath ODM table)

fcs3 (wwn 71cb) -> no devices configured behind this fscsi3 driver
instance (path only configured in CuPath ODM table)

fcs0 (wwn 71e4) -> no devices configured behind this fscsi0 driver
instance (path only configured in CuPath ODM table)

fcs1 (wwn 71e5) -> ALL devices configured behind this fscsi1 driver

Looking at the MPIO path configuration, here is what we have for the rootvg disk:

# lspath -l hdisk2 -H -F”name parent path_id connection status”

name parent path_id connection status

hdisk2 fscsi0 0 5006048452a83987,33000000000000 Enabled

hdisk2 fscsi1 1 5006048c52a83998,33000000000000 Enabled

hdisk2 fscsi2 2 5006048452a83986,33000000000000 Enabled

hdisk2 fscsi3 3 5006048c52a83999,33000000000000 Enabled

The fscsi1 driver instance is the second path (pathid 1), then remove the 3 paths keeping only the path corresponding to fscsi1 :

# rmpath -l hdisk2 -p fscsi0 -d

# rmpath -l hdisk2 -p fscsi2 -d

# rmpath -l hdisk2 -p fscsi3 -d
# lspath -l hdisk2 -H -F”name parent path_id connection status”

Afterwards, do a savebase to update the boot lv hd5. Set up the bootlist to hdisk2 and reboot the host.

It will come up successfully, no more hang LED 554.

When checking the status of the rootvg disk, a new hdisk10 has been configured with the correct ODM definitions as shown below:

# lspv

hdisk10 0003027f7f7ca7e2 rootvg active

# lsdev -Cc disk

hdisk2 Defined 00-09-01 MPIO Other FC SCSI Disk Drive

hdisk10 Available 00-08-01 EMC Symmetrix FCP MPIO Raid6

To summarize, it is recommended to setup ONLY ONE path when installing an AIX to a SAN disk, then install the EMC ODM package then reboot the host and only after that is complete, add the other paths. Dy doing that we ensure that the fscsiX driver instance used for the boot process has the hdisk configured behind.

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