Multipath tape drives intermittenly go DOWN on AIX media server.

Problem

Multipath tape drives intermittenly go DOWN on AIX media server.

Error Message

In the ltid log (/usr/openv/volmgr/debug/ltid) can be found a mount request which got canceled in 15 minutes with error 9 and then the drive was downed -
04:19:51.985 [8913144] <4> tpreq: User tape request: RVSN:<media> EVSN:<media> Drive:<drive> Path:<path> AttachHost:
04:19:51.985 [8913144] <4> IssueMount: mounting on drive <drive> path <path>
...
04:34:39.301 [8913144] <4> ProcessRobotMsg: Sending robotic error 9 to BPTM
04:34:39.301 [8913144] <2> CancelMount: Mount request canceled for media id <media>

and then the drive went down -
04:34:47.361 [8913144] <6> DownDrivePath: DOWNing path <path> for <drive> on host <host>

Cause

When using devices with Multipath I/O enabled, NetBackup does not detect that the path has switched to an alternate one, and downs the drive.

 If Atape driver's Data Path Failover feature is enabled on the drives, NetBackup will intermittenly down the drives, when the path fails over to the alternate path.

Refer to the NetBackup 7.x Hardware Compatibility List  where on page 109 step number 6 and at the end of page 164 it says the following:
AIX was tested using the IBM Atape device drivers.
- Atape 12.5.9.0 driver tested on AIX 6.1 and 7.1. NetBackup does not support the driver's Data Path Failover feature.
 

To check if the Atape driver's Data Path Failover feather is enabled on your devices, run the following command on each tape drive's device file -

lsattr -El rmtX

Look for the parameter called alt_pathing, if it is set to 'yes', then this feature is enabled.

For example,

lsattr -El rmt1

alt_pathing      yes                Enable Alternate Pathing Support      True

This indicates that Atape driver's Data Path Failover feature is enabled on drive rmt1.

Solution

Disable Atape driver's Data Path Failover feather on all drives by running the following command -

chdev -l rmtX -a alt_pathing=no

Or use smit menu to select Change/Show Characteristics of a Tape Drive, then select No for Enable Path Failover Support.

NetBackup will on its own choose either a primary or alternate path to the drive even with this feature being disabled.

Applies To

AIX media server with IBM 3580 Ultrium Fibre Channel tape drives having 2 device files for each path to the tape drives.

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