topic Re: need explanation of application snapshot in StoreVirtual Storage

need explanation of application snapshot

pob579 — Wed, 07 Dec 2011 02:14:16 GMT

Hello,

please explain application snapshot feature. Practical use and advantages.

I used a lot snapshot (checkpoints) in hyper-v for having the ability to come back to previous OS state.

Does application snapshot relates to backup? How we use it in P4000 environment?

Thx.

Re: need explanation of application snapshot

HenryLee — Thu, 08 Dec 2011 16:13:16 GMT

We just installed this same unit and I'm currently working to understand the snapshots myself. I'm a SQL Server DBA so take my comments in that context.

The application managed snapshot quiesces the application, the point in time does not. Quiesce is a fancy word for pausing writes so you get a consistent view of the data.

The snapshots are super fast, like instant, because they are just pointers back to the original data. Subsequent snapshots track any changes. Because these snapshots are simply pointers (and not a compete copy of the data), they are depenent on the original data being available. So this can protect you against logical problems (in my case, someone drops a table), however, they don't help if anything happens to the original volume or LUN. So you still need to backup to a secondary location.

Again, this is my understanding after only a month or so with the unit. Please take with a grain of salt.

Re: need explanation of application snapshot

Robert Lennie — Thu, 08 Dec 2011 20:59:52 GMT

Almost a 100% ;) Yes - the P4000 supports VSS aware snaps, as well as ESX snaps in SAN/iQ 9.5. So, yes the application aware snap is not only a point in time but applicaiton consistent.

The original volume will always be protected because all new writes (which are the only things that can corrupt a volume) go to new blocks. When the next snap occurs, that is just another layer ontop of the old lun - therefore you can mount different points in time.

Re: need explanation of application snapshot

pob579 — Fri, 09 Dec 2011 03:02:34 GMT

Thanks!

Robert, I marked Henry's answer as a solution. Anyway you confirm that his answer is Almost 100% accurate.