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Full Name: Chris

Do backups create dirty blocks on SAN?

Post by cparker4486 »


The Snapshot Reserve Space on my EqualLogic SAN is being used up much more quickly than I would expect it to be and I wonder if this is due to Veeam making the virtual machine file blocks dirty.

I'm not talking about the vbk/vrb files that Veeam generates I'm talking about the virtual machine files themselves.
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Re: Do backups create dirty blocks on SAN?

Post by Gostev »

Hi Chris, no - our product is read-only as it comes to pulling VM snapshot data from the storage during backup. Thanks.

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Full Name: Tom Sightler

Re: Do backups create dirty blocks on SAN?

Post by tsightler »

Equallogic snapshots eat space like a bear coming out of hibernation because, unless they've changed something in recent code versions, they use a 16MB block size. That means a single 4K block changed on a filesystem will cause a 16MB stripe copy for the snapshot. Just do a Google search about it and you'll get plenty of hits, here's just one example:

However, if you are taking snapshots of the VMFS volumes then of course Veeam creating VMware snapshots will cause some additional growth as well because, while the snapshots are open, writes have to go into new files which reside on additional areas of the VMFS volume rather than back to the original VMDK location. But generally, snapshot growth on Equallogic is a problem whether you're using Veeam or not.

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