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VMWare volume, 16% space savings, should it be higher?

HendersonD
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I have a 2TB volume on a FAS3020 running OnTap 7.3.2. This volume is shared via NFS and is added as storage for my ESXi 4.1 hosts. I have 29VMs stored on this NFS share, a mixture of Win2003 and Win2008 servers. I have had dedup enabled on this volume for several months. At the command line of the filer I ran:

df -s /vol/VMWare

It says there is a 16% space savings. This seems low. I thought I had read other accounts, as well as Netapp marketing material, that claims space savings for VMWare in the 40-50% range. Any ideas?

I do take snapshots on this volume using SMVI but as I mentioned I have had dedup turned on for months and only keep a few weeks worth of snapshots.

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datamanaged
16,918 Views

Hi Again Hendersond,

I'm not sure if my math is 100% correct here, but its not far from it.

Total volume usage - Snapshot Usage = Live Data

Dedupe Savings / (Live Data + Dedupe Savings) = Dedupe ratio excluding snapshots

For you:

1068 - 773 = 295

244 / (295 + 244) = 45.2% saved

The 19% you're seeing is based off of the 244GB of savings on 539GB of live data with an overhead of the snapshots 773GB (and for some reason it treats the snapshots as undeduped, when in reality they probably *are* deduped). If we factor snapshots into the above equation: 244 / (295+244+773) we get 19% after rounding.

We actually just noticed this with our DFM provisioning manager, whereas the CLI shows the dedupe saving including snapshots as just used storage, DFM seems to exclude snapshots from its computations. Our VSphere volume is ~42% saved in the CLI in DFM its abou 52% ( we have a very short backup schedule)

If you really want to tell, delete your snapshots(prolly not a good idea though). Alternatively, just try deleting a number of snapshots off the tail end (such as all of november if you don't need them). This might give you an idea of how the dedupe % will fluctuate.

Long story short, its a bit of bad math in df -s in combination with your snapshots.

I hope we've answered the conundrum at this point. If you still have problems our questions, let us know.


Best Regards,

Adam S.

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