topic Re: Windows clients not seeing deduplication savings in ONTAP Discussions

Windows clients not seeing deduplication savings

GRIMSTONER — Wed, 04 Jun 2025 22:04:37 GMT

I have an 8 blade Windows Hyper-V 3 cluster. Each of these blades has access to a 5.00Tb LUN (Cluster Shared Volume), created through Snapdrive, stored in a 5Tb volume, where each of my 80-odd virtual machines' vhdxs are stored:

Vol

Lun

Storage efficiency is enabled, and after the last run, these are the results:

However, Windows still reports only 439Gb of free space:

I don't have any snapshots or QoS setup on this volume.

Now:

The vol reports that it has 2.42Tb free space (due to dedupe I assume)
The lun reports that it has 1.11Tb of free space
Windows only reports that there is 418Gb of free space...

Where did the other 718Gb go that's supposed to be left in the LUN?

How much can I safely decrease the size of the volume now that it is deduped?

Re: Windows clients not seeing deduplication savings

Renifa — Mon, 15 Feb 2016 10:29:39 GMT

Hi,

Chances are there that VMware had not reclaimed the free blocks due to which you have the size difference. Use the VMware reclaim tool to resolve this issue http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&externalId=2014849

Hope this helps.

Re: Windows clients not seeing deduplication savings

GRIMSTONER — Mon, 15 Feb 2016 10:34:58 GMT

I'm using Hyper-V, which means I use the Space Reclamation tool in Snapdrive.

However, when invoking the tool, this is displayed:

So space reclamation won't make a difference.

Re: Windows clients not seeing deduplication savings

paulstringfellow — Mon, 15 Feb 2016 14:23:43 GMT

Hi, the issue you have here a bit of a misunderstanding on where dedupe works.

The dedupe saving are purely at a block level within the NetApp volumes.

These are not seen at all by Windows.

I assume the reason you only see the free space you do under windows is because the VHD files take up 4.5 Tb within the csv.

Leaving you with ~500GB of free space.

The LUN and volume capacity you can see at the controller level is based on the NetApp space savings, but these are not seen by windows, it just sees what it does in the csv.

Hope that helps.

Re: Windows clients not seeing deduplication savings

JamesIlderton — Mon, 15 Feb 2016 20:35:32 GMT

Yes, he is correct. If order to "see" the real available space, you would need to use CIFS shares over SMB 3.0 for your Hyper-V storage. This way, NetApp's WAFL is handling the underlying filesystem instead of Windows and it has visibility into the actual free space. It has other added benefits as well, take a look at http://www.netapp.com/us/media/tr-4172.pdf for more details.

Re: Windows clients not seeing deduplication savings

paulstringfellow — Mon, 15 Feb 2016 23:07:25 GMT

Again this is correct, you do need to be running clustered OnTap for this, feature not available in 7-mode. You'll want to check which versions of cdot 8.2 onwards i think, check the interoperability matrix to be sure.

Hope this all helps.