Posts Tagged ‘EVA SSSU’

HP EVA SSSU and fixed LUN WWID

Monday, July 14th, 2008

Linux works perfectly well with multiple storage links using dm-multipath. Not only that, but HP has released their own spawn of dm-multipath, which is optimized (or so claimed, but, anyhow, well configured) to work with EVA and MSA storage devices.

This is great, however, what do you do when mapping volume snapshots through dm-multipath? For each new snapshot, you enjoy a new WWID, which will remap to a new “mpath” name, or raw wwid (if “user_friendly_name” is not set). This can, and will set chaos to remote scripts. On each reboot, the new and shiny snapshot will aquire a new name, thus making scripting a hellish experience.

For the time being I have not tested ext3 labels. I suspect that using labels will fail, as the dm-multipath over layer device does not hide the under layered sd devices, and thus – the system might detect the same label more than once – once for each under layered device, and once for the dm-multipath over layer.

A solution which is both elegant and useful is to fixate the snapshots’ WWID through a small alteration to SSSU command. Append a string such as this to the snap create command:

WORLD_WIDE_LUN_Name="6300-0000-0000-0000-0010-0000"

Don’t use the numbers supplied here. “invent” your own 🙂

Mind you that you must use dashes, else the command will fail.

Doing so will allow you to always use the same WWID for the snapshots, and thus – save tons of hassle after system reboot when accessing snapshots through dm-multipath.

HP EVA bug – Snapshot removed through sssu is still there

Friday, May 2nd, 2008

This is an interesting bug I have encountered:

The output of an sssu command should look like this:

EVA> DELETE STORAGE “Virtual DisksLinuxoracleSNAP_ORACLE”

EVA>

It still leaves the snapshot (SNAP_ORACLE in this case) visible, until the web interface is used to press on “Ok”.

This happened to me on HP EVA with HP StorageWorks Command View EVA 7.0 build 17.

When sequential delete command is given, it looks like this:

EVA> DELETE STORAGE “Virtual DisksLinuxoracleSNAP_ORACLE”

Error: Error cannot get object properties. [ Deletion completed]

EVA>

When this command is given for a non-existing snapshot, it looks like this:

EVA> DELETE STORAGE “Virtual DisksLinuxoracleSNAP_ORACLE”

Error: Virtual DisksLinuxoracleSNAP_ORACLE not found

So I run the removal command twice (scripted) on an sssu session without “halt_on_errors”. This removes the snapshots correctly.