PowerPath AIX LPM and errpt message question

Incidentally, which version of PP are you on and which ODM files do you have installed?

PowerPath uses a unique identifier for each detected device-path pair.  With LPM, you migrate the disk from one set of logged-in host initiators to another set of host initiators.  From PowerPath's perspective, the host device isn't accessible on the current device-path and marks it unavailable.  PowerPath sends errors to the errpt facility and get flagged as such.

You might want to test things by looking at the device state with powermt display dev=all prior to the LPM event.  Note the devices and their path states.  Then, execute the migration and check powermt display dev=all output again.  I syspect you will need to run powermt restore to recheck paths to disk, then powermt config to configure new paths.

Let us know if that helps!

Karl

Temporary dead paths are an expected condition during an LPM operation.

As per EMC Engineering: "the original HBAs switch to the alternate HBAs, thereby causing a [temporary] failed path".

Setting reserve_policy to no_reserve is mandatory for all of the hdiskpower devices as well as their underlying hdisks.

There should be no need to run a powermt restore as the paths should recover automatically.  However as Karl stated, good housekeeping would dictate that you run a powermt display dev=all before and after the LPM operation to verify path integrity.

The following EMC Knowledge Base articles have some further information on potential LPM issues:

000454413

000439567

000439265

Hi Karl - We're running AIX 7.1 - PP 6.0 & ODM 6.0.0.5. Also, we're

running our LPARs through a 4 engine VPLEX to a VMAX & also we use NPIV.

We have 8 paths to each VMAX lun. We run a powermt display before & after

the migration and both are all clean. Our concern is that sometimes all 8

paths show as offline for 1 second or so in the errpt.

From:

brn_lewisk

To:

halt2000

Date:

04/19/2016 01:48 PM

Subject:

Re: - PowerPath AIX LPM and errpt message question

ECN

PowerPath AIX LPM and errpt message question

reply from Karl in PowerPath - View the full discussion

Incidentally, which version of PP are you on and which ODM files do you

have installed?

PowerPath uses a unique identifier for each detected device-path pair.

With LPM, you migrate the disk from one set of logged-in host initiators

to another set of host initiators. From PowerPath's perspective, the host

device isn't accessible on the current device-path and marks it

unavailable. PowerPath sends errors to the errpt facility and get flagged

as such.

You might want to test things by looking at the device state with powermt

display dev=all prior to the LPM event. Note the devices and their path

states. Then, execute the migration and check powermt display dev=all

output again. I syspect you will need to run powermt restore to recheck

paths to disk, then powermt config to configure new paths.

Let us know if that helps!

Karl

Reply to this message by replying to this email, or go to the message on

ECN

Start a new discussion in PowerPath by email or at ECN

Following PowerPath AIX LPM and errpt message question in these streams:

Inbox

CONFIDENTIALITY NOTICE: This email message and any attachments are for the sole use of the intended recipient(s) and may contain proprietary, confidential, trade secret or privileged information. Any unauthorized review, use, disclosure or distribution is prohibited and may be a violation of law. If you are not the intended recipient or a person responsible for delivering this message to an intended recipient, please contact the sender by reply email and destroy all copies of the original

message.

Thanks Karl -> powermt display looks fine before & after the LPM.  We're just concerned about the errpt messages.  IBM says we should only see migration started/migration completed.  I guess we're wondering what do other people see in errpt using PP?

Hi Halt2000,

when migrating an LPAR from one server to another, there is a period (<1 second) when the original WWNs switch to the backup pairs - thereby causing a very brief path down condition.

Once PP receives a failed IO from the underlying SCSI driver layer, it will report the path as dead and commence path testing.

Once the path is recovered, PP will mark the path status as alive/active.

So in an LPM scenario such as this, PP is working exactly as expected.

How do you explain the fact that during some LPM Migrations we see database disk errors in the database logs and unable to communicate with device messages in the aix errpt?