topic Overcomitting a LUN to use deduplication savings in a Volume? in ONTAP Discussions

Overcomitting a LUN to use deduplication savings in a Volume?

tomas_netherlands — Thu, 05 Jun 2025 07:17:33 GMT

I am trying to figure out how to reuse the dedupe savings in a volume with 1 LUN.

I am using Hyper-V CSV where the space saving is about 50%.

I want to use this space within this LUN. Is it possible to overcommit the LUN on the volume.

Is someone else using another "best practice" or what would you advise me to do?!

The CSV vol AND LUN are 700 GB, after dedupe there is 350GB in use in the VOL. Lets say i want to add 200GB to the lun and make it 900 GB without space reservation making it thin.

In this way the volume shows 700 GB and the LUN shows 900 GB.

Is this going to work?!

Tomas

Re: Overcomitting a LUN to use deduplication savings in a Volume?

Sebastian_Goetze — Fri, 19 Mar 2010 10:52:15 GMT

I'd say Thin Provision your volume (space guarantee none or file) and make it a little bigger than your LUN.

(It's possible to create a thin-provisioned LUN bigger than the containing volume - I just tried it - but I'd consider it Bad Style...)

But also check page 32 in the current Dedupe-Dig (tr-3505) 'DEDUPLICATION AND LUNS', for the different combinations of the LUN space guarantee, Vol space reservation and fractional reserve settings for where your dedupe-freed blocks go (Overwrite reserve/Volume/Aggregate).

HTH

Sebastian