Dedupe with VMware

Subject: Private Message: Re: Dedupe with VMware


Glad to help. That is working as expected with LUNs and VMware. With LUNs VMware used their VMFS file system which expects a fixed number of blocks and doen't understand dedupe. This means that when you dedupe the volume the LUN and VMFS will still appear full. You now have to decide what you want to do with all that space you just got back. You have 2 options. You can grow the LUN, this will make the LUN bigger but not VMFS. You would then add a VMFS extent to the LUN and then you can use the new space.

Personally though I don't like extents as I have had some bad things happen. Instead I would shrink my volume. This will release space back into the Aggregate and allow you to create a new volume and a new LUN. You won't want to shrink the volume back all the way to the new LUN size as you will need room for a little dedupe space but perhaps the new LUN size plus 15-20%. Then create a new Volume and place a LUN in it. This time though when you create the LUN don't space reserve it and make it bigger than the volume.

I don't know your exact numbers but lets run through a sample scenario.  So your volume is 420 GB and your LUN is 400GB. You turned off LUN reservation and deduped and say now your LUN in 100GB in size. You can then reduce your volume to 140GB (20GB for reduplication and 20GB for snapshots) or something similar to that. Giving you 160GB in your aggregate. If you create a new 140GB volume and place a 400GB LUN in it. You now have 400GB more space for your VMs, and still have 20GB extra on your aggregate to use where needed. YOumight add 10GB to each volume just to be safe or leave it in the aggr and set the volume to autogrow if needed.

You will want to carefull deploying VMs to the new LUN as they will take up full space until you dedupe them so don't try to push out 20 new VMs! but use it slowly and perhaps kick off a few extra dedupe passes as you push VMs out.

Make sense?

Would I be able to post this on the forum as it is a great question and one I am sure other folks have.


Hi Keith,

I'm new to dedupe and would like to ask you a question if you'd be so kind to respond. We have run dedupe on a 420 GB volume that has a 400GB LUN with .vmdk files located on it. When we run dedupe, we see a huge savings in disk space 83%. However when we look at the datastore within VC we don't see the reclaimed space. We don't have space reserved checked within the LUN we de-duped.

Any help would be much appreciated.



Re: Dedupe with VMware

Excellent answer -- there's also a good doc in the NetApp Community available here (ironically I just emailed it to a customer last night).