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Snapshots in ESX Server on on the Array?

Posted on 2008-10-03
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Hi Guys
I'm looking at virtualising some of our servers but have been scaratching my head over taking snapshots. what is the best way of impklenting these. through Esx server itself or taking the snapshots on the array. The San that i'm looking to purchase is the Dell Equallogics PS5000X and i believe this has software capable of taking snapshots of servers SQL and Exchange.

Any ideas would be welcomed
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Question by:staylor1972
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HeinoSkov earned 125 total points
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Hi, snapshots in ESX is only for temporary usage, because it creates a delta file which can grow and grow and grow. This would leave a huge risk on running low on storage if esx snapshots are used in a more common way.

Array-based snapshots would be to prefer, again it depends on what you need to do with the snapshots. If using VMFS then you would need to retrieve the whole LUN from the snapshot to the ESX to get the data back. You could use RDMs to raw device mappings to with array based snapshots to get the features from snapshots you want to use with SQL / Exchange.
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by:HeinoSkov
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Just keep in mind that you have a virtualized layer in between that you need to present the snapshot'ted LUNs to.
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by:robocat
robocat earned 125 total points
ID: 22632620

ESX snapshots and Array snapshots are complementary.

ESX snapshots can easily rolled back, so these are ideal in case of planned changes. E.g. take a snapshot before you install patches inside a VM if you want to be able to undo these changes quickly. ESX snapshots should not be kept longtime.

Array snapshots are more a protection against logical corruption or accidental deletion of your VMs but it's more difficult to restore from a snapshot.

Remember that snapshots always have some kind of performance penalty (except if you go for a NetApp array).




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by:valheru_m
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Be VERY careful using snapshots on exchange and SQL databases (or any other database that maintains state information for that matter).  If you take a snapshot on a machine with a running exchange or SQL database, reverting to that snapshot will only give you a crash-consistent copy of your database.  This is because databases are constantly being written to and often have cached data that has not been flushed to disk. If you need to take a snapshot of any server running these services, make sure that the exchange and/or sql services have been safely stopped before taking the snapshot to avoid potential severe database corruption.
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by:HeinoSkov
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That count as Active Directory servers as well :-)
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by:andyalder
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Snapshotting won't truncate the Exchange or SQL transction logs either, they'll just grow and grow.
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by:staylor1972
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Is there any software for ESX server that will allow you to get Exchange or SQL into a safe state before you take a snapshot, without having to stop the virtual server to take the snapshot?
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by:robocat
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I'm not aware of any software on ESX level that will do this kind of integration. Of course you can always do your own scripting.

For Storage environments, most big vendors (NetApp, I think also EMC, ...) have software product that tightly integrate with Exchange/SQL to take consistent snapshot backups and also allow e.g. partial restores of databases/single mailboxes from snapshots.

I'm not sure if Equallogics can do this.

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