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Dedup only saving 5% on 750gb of windows VM's

I currently have two ESX 3.5 hosts connected to a 2050 running 7.3.1.1 through iscsi.  I recently had to create a brand new lun and migrate all of my VM's to it becasue the vmfs file system became corrupted.  On my old lun dedup was saving me 65% of my space but on the new one I am only saving 5%.  It is a 1 TB volume with space settings set to volume, fractional space reservation set to 0% and snapshot reserve set to 0%.  On the Lun space reservation is turned off.  I have set dedup to run between 3 and 6 am everyday and it now seems to take 6 min to run every night.  I can't figure out why this would have changed.  Any help would be apreciated.

Re: Dedup only saving 5% on 750gb of windows VM's

Hey Wally,

You might want to check that no snapshots have been taken - did you set the snap schedule to 0 0 0 on the new volume created before migrating the VMs over? (snap sched <volumename> 0 0 0). 

If there are snaps residing on that volume the data will be locked and dedupe will not touch the data until the snap releases it (i.e. snapshot deleted).

Other than that I'm not sure, I'll have a think...

Re: Dedup only saving 5% on 750gb of windows VM's

A few thoughts.....

  • Generally speaking (not related to the actual issue), NFS does expose deduplicated space more easily (no frac reserve, shows directly in the VI client, etc.).
  • If you deploy 2 new VM's from the same template (no need to power them up), check "df -Sh", run dedup, "df -Sh" again, what do you see? (should get a lot of space back)

Re: Dedup only saving 5% on 750gb of windows VM's

Yes you should of course see 65% savings on the new LUN just like you did on the old LUN.  Your LUN settings seem correct.  Question, did you run the "sis on" command on the volume before you did the migration, or run "sis start -s" on the volume after the migration?  You'll have to have done one or the other to get the full dedupe savings.

DrDedupe.

Re: Dedup only saving 5% on 750gb of windows VM's

I reckon you need to set vol guarantee to none. Can you look in old autosupports to set what the old volume used to have? you find old asupsin /etc/log/ folder on controller.

If you are worried about writes to your LUN you can then use "vol autosize" command so that the volume will grow when

the LUN needs space. We use this config and it works like a charm. This config forces free blocks back to

aggr. level = easier to monitor/monitor.

So long you dont use snapshots you dont have to worry about "snap autodelete" once/if the volume reaches its max size.

Cheers,

Eric

Re: Dedup only saving 5% on 750gb of windows VM's

If there are snaps residing on that volume the data will be locked and dedupe will not touch the data until the snap releases it (i.e. snapshot deleted).

It actually behaves in a slightly different way:

if there is even a single snapshot in the volume in question, then de-dupe will show whatever savings has been made, but the snapshot will grow by exactly the same figure as the "saving".

So the bottom line is that the described behaviour is weird, as even with snapshots in the volume in question, de-dupe "savings" ought to be measurable.

Regards,

Radek

Re: Dedup only saving 5% on 750gb of windows VM's

I reckon you need to set vol guarantee to none.

That's bad idea, as vol guarantee set to none enforces 100% fractional reserve (can't be changed).

Vol guarantee set to volume (plus vol auto-size & snap auto-delete, plus FR of 0%) & thinly provisioned LUNs within that volume is a way to go!

Regards,

Radek

Re: Dedup only saving 5% on 750gb of windows VM's

On my old lun dedup was saving me 65% of my space but on the new one I am only saving 5%.

Isn't your block alignment screwed up by any chance? That may explain poor dedupe ratio (I think)

Re: Dedup only saving 5% on 750gb of windows VM's

Hi Radek,

By setting it to none you can start monitoring your space at aggregate level as opposed to have to monitor X numbers of volumes. It obviousily a lot

easier and allows for cap. planning to be facilitated at the same time.

However for some customers setting vol guarantee to none is not good of course. I just think any statement that categorically states

its not good to set it to none will not be right 100% of the time. it does work for us, in fact I love it! :-0

Cheers,
Eric

Message was edited by: eric barlier

Re: Dedup only saving 5% on 750gb of windows VM's

I have not heard that block align. issues will impact on dedupde savings. Dedupe is at WAFL level and the block un-alignment issue is when you put

a file system on top of WAFL and its not aligned = impact on perf.

Its an interesting thought though. Does anyone hold conclusive information about this? Is Radek onto something here?

Cheers,
Eric