Snapshot cache problem

Hello,

You can not assign a cache LUN to a secified LUN.
The only worry workaround would be that you remove the cache luns from the reserved lun pool; before starting the snapshot of lun A you add the cache lun A1 to the reserved lun pool. then start the snapshot of lun A --> and then the same game for lun B....
See also "EMC Clariion Reserved LUN Pool Configuration Considerations." Document at powerlink.
best regards
Manfred

Snap Cache LUN is not for any specific snapshot session - the cache LUNs are configured in a pool (Snap Cache Pool which is now named as Reserved LUN Pool) - per Storage Processor. These LUNs are of much smaller size - so that the space utilization for snap is quite high. You should not be worried about the size of one specific Snap Cache LUN which is assigned for a particular snap session - if one LUN is full - it will automatically allocate space from another LUN in the reserved LUN pool of that SP. Make sure you have sufficient small sized LUNs in the reserve LUN pool of each SP.

For a given Source LUN - you need at least one Private LUN in the reserve LUN pool on the same SP to start the snap session. Any subsequent sessions for the same source LUN may use the same Private LUN (Cache LUN) - but for a different source LUN, at least another free (unused) cache LUN is required in the pool.

Please note that the same Reserve LUN pool is used not only with snap sessions but with other applications like SANcopy and Mirrorview asynchronous.

Please refer to SnapView administration Guide or related White papers on Powerlink for more information.

Hope this helps,
Thanks,
Sandip

You cannot assign Snapcache to a specific lun, I would increasing the amount
of snapcache available. Or try running the session at a different time from any other snaps to ensure no other session is using cache.

The most practical solution is to increase snap cache.

Adrian

Message was edited by:
ASR

It's a matter of trial and error. Find out what the size of a savlun was when your snapview session "crashed" and try to figure out how large the savlun had to be to survive the write I/Os produced by the source lun. Remove all sav luns and create new, bigger ones. IMHO you shouldn't use savluns of different sizes, since you cannot predict what savlun a snapview session is going to use, so if having 50 sav luns of 5GB each isn't enough, delete them and create 50 new ones of let's say 6, 7 or 7.5GB or something. In the beginning this can be a lengthy process, but in the end you'll find out what's good for you.

Message was edited by:
RRR
Each Clariion type has a different number of maximum sav luns. If you haven't created this maximum yet, create more if a snapview session stops. A snapview session that claimed a sav lun wil take a 2nd sav lun if needed and a third, fourth and so forth, but if there are no more sav luns to take, the session will "crash".