SAN Snapshot Restore

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SAN Snapshot Restore

Veeam Logoby deduplicat3d » Mon Aug 27, 2012 4:43 pm

I read about the upcoming feature in this week's digest. I had one quick question out of curiousity: is there some way that the snapshot gets quiecsed so that there are good restores? In my experience SAN snapshots tend to be an instant in time without quiecsing, but that seems a bit inconsistent with Veeam.
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Re: SAN Snapshot Restore

Veeam Logoby Gostev » Mon Aug 27, 2012 5:50 pm

HP SAN/iQ does support optional quiescing of VMs on SAN snapshots, they call this option "application-managed snapshot". You will see this in the snapshot scheduling UI - as well as in Veeam UI where we provide ability to create SAN snapshot manually.

This is not necessarily something I personally would always use though. For example, if you scheduled periodic SAN snapshots every hour, any sort of application-level quiescing might have quite noticeable impact on some services during production hours.

Crash-consistent snapshot should be fine most of the times. And for those rare cases when those SAN snapshot restore points would not recover, you still have good, consistent restore points that are properly quiesced with application-aware processing, as well as SureBackup-tested for 100% guaranteed recovery. I am talking about real backups you would still continue taking daily during off-hours with Veeam backup jobs.
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Re: SAN Snapshot Restore

Veeam Logoby deduplicat3d » Mon Aug 27, 2012 7:24 pm

Yeah I wouldn't want to have everything quiescing every hour :-/

Everything you said makes sense. I use Equallogic so I haven't seen the HP UI... but hopefully you expand the SAN Snapshot technology to Equallogic!!

Love the stuff you guys are doing.
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Re: SAN Snapshot Restore

Veeam Logoby Gostev » Mon Aug 27, 2012 9:28 pm

Believe or not, but our original intention was to have EqualLogic the first storage we support with this functionality, and we even had to invest and buy the unit for our lab (Dell just would not give it to us for free, like all of our other storage partners do). :D

However, hands on testing in our labs showed that EQL's implementation of snapshots is extremely inefficient - both in terms of disk space EQL snapshots use (due to 16MB block size), and significant performance overhead running off snapshot chain. Because these limitations would prevent most customers from enabling periodic SAN snapshots, this kind of ruins the whole concept - so it made no sense to built our snapshot restore functionality around this particular SAN.

Now, with EQL being out of the picture, since we already had established relationship with HP storage team (over our HP StoreOnce partnership), it was natural to take a look at their production storage next. They provided us LeftHand units, and we found their snapshot implementation to be much better than in EQL. We also liked that they ship the same code as StoreVirtual VSA, providing all the same enterprise-class SAN functionality at much lower price point - which seemed to be a natural fit with big part of our existing customer base.
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Re: SAN Snapshot Restore

Veeam Logoby deduplicat3d » Tue Aug 28, 2012 8:39 pm

So sad to hear that! I have never used snapshots on my equallogic because, why bother when you have Veeam. Restoring an entire volume to a previous state just did not go well with me.

I hope that Dell improves, maybe even with them rolling out firmware v6 :)
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Re: SAN Snapshot Restore

Veeam Logoby sketchy » Mon Dec 03, 2012 1:27 am

Gostev wrote:Believe or not, but our original intention was to have EqualLogic the first storage we support with this functionality, and we even had to invest and buy the unit for our lab (Dell just would not give it to us for free, like all of our other storage partners do). :D

However, hands on testing in our labs showed that EQL's implementation of snapshots is extremely inefficient - both in terms of disk space EQL snapshots use (due to 16MB block size), and significant performance overhead running off snapshot chain. Because these limitations would prevent most customers from enabling periodic SAN snapshots, this kind of ruins the whole concept - so it made no sense to built our snapshot restore functionality around this particular SAN.


Huge fan of Veeam here. But also an experienced EqualLogic user for many years. I would love for you to expand on that notion of innefficiency on the EqualLogic snapshots. Not in the block size (well documented) but the "signifigant performance overhead running off snapshot chain." This is simply not true. At the time that EqualLogic came to be, most other SAN vendors were doing a "copy on write" strategy for SAN based snapshots. THIS is what lead to performance issue especially when they got beyond a handful of snaps. EqualLogic has always used a "reassign on write" (aka re-allocate on write) which elliminates this "chaining" issue with SAN based snapshots. The result is virtually limitless numbers of SAN snapshots with zero performance degradation.

I'm anxious for Veeam to come out with integration with EqualLogic as well. I'm sure that without doubt, each SAN vendor presents certain challenges when attempts to integrate them occur. I just question this actual explanation.

Would love to hear a response.
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Re: SAN Snapshot Restore

Veeam Logoby Gostev » Tue Dec 04, 2012 2:41 pm

Hi Pete,

We have tested both Equallogic and LeftHand extensively in-house, and performance was mostly the same except when snapshots were enabled. With snaps on, LeftHand provided approximately 3x better random write IOPS than Equallogic.

However, the performance issues are not as critical as the real show stopper. Equallogic snapshots required about 20x more space. Both problems seem to be caused by a very large block size, and collectively they render the whole data protection concept mostly unusable.

While performance issue may be resolved by now, as the testing was done well over a year ago, the disk space usage is really a blocking factor for our typical customer.

Thanks!
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