Windows Deduplication over iSCSI on Synology

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MarP
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Windows Deduplication over iSCSI on Synology

Unread post by MarP » Mon Sep 24, 2018 1:54 pm

Hi All,

I have 3 x 4TB LUNs on Synology. All of them are connected by iSCSI to Windows Server 2012 R2. A few weeks ago I've set up Windows Deduplication over those drives as there was only ~200GBs free on each.

After Dedup I have about 1.5TB free in Windows - thats cool. But Synology on LUNs summary showing Reported: 4TB, Used: 4TB. It looks like no space was reclaimed after dedups. Yesterday I had a need to remove one LUN as LUNs were Thin Provisoned and I've reach out the limit. Drama! :evil:

Each weekend GC and WS are running.
Scheduler showing about 3h of working WeeklyGarbageCollector and about 2h of WeeklyScrubbing.

Any hints?

Cheers,
MARP

Squozen
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Re: Windows Deduplication over iSCSI on Synology

Unread post by Squozen » Mon Sep 24, 2018 2:49 pm

You won't gain space back unless Windows instructs a SAN to reclaim blocks (either by using an API or by actually zeroing unused blocks) - the Synology has no idea what the filesystem contains and an previously-used block on the Windows filesystem still contains data as far as the Synology can tell. Windows 2012 R2 should zero blocks eventually by itself but you can force the issue by using a utility like SDelete which should trigger a reclaim from the Synology.

https://docs.microsoft.com/en-us/sysint ... ds/sdelete

The -z flag is the one you're after.

If you're still not seeing a shrink occur after running SDelete then something is definitely wrong.

edit: in Defrag & Optimize Drives in Windows, check that the disk is showing as a Thin provisioned drive.

MarP
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Re: Windows Deduplication over iSCSI on Synology

Unread post by MarP » Tue Sep 25, 2018 5:12 am

Thanks @Squozen! I suppose this is the thing I need.
Can you also advise of two things:
  • What impact it has on performance? Means - nightly, during workday or weekends?
  • Approximately what time it needs to get zeroed the 1TB of free space over 2x1Gbit connection?
Thanks a lot!

Edit: Yes, media type = Thin provisioned drive.

MarP
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Re: Windows Deduplication over iSCSI on Synology

Unread post by MarP » Tue Sep 25, 2018 9:06 pm

Hi,

Just made a test.
4TB LUN, 1,3TB free of 4TB. Put sdelete -z on drive. After 20% passed Windows showed 1,07TB free. and Synology same 4TB reported/4TB used. Braking the sdelete process instantly gives back the missing 0,26TB.

Any hints?

Cheers,
MP

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