Configuring NetApp Deduplication With LUNs

by NetApp on ‎2008-05-20 03:59 PM - edited on ‎2014-09-26 12:55 PM by alissa Netapp Alumni

Deduplication creates free space, but where does the free space go? The paper describes 5 basic LUN configurations and the different results that occur once space is reclaimed by deduplication.


Awesome document - really helped in making a decision for implementation


Hi Larry,

Very interesting !!

However does it mean that NAS protocols (CIFS and NFS) are the only way to make  Attached OS be able to know deduplication has occur and take space saved into consideration in their own kernel ( management tool)

Can you please confirm :

Presenting a NFS Share to an AIX host for example :

1 : let's say 300 Go and 100 Go are filled.

2 dedup is running and DataOntap says 50 % gain on that volume (meaning 250 Go are now Free)

Result : AIX is still connect to a 300 Go share on which 250 are Free ?? That's it ??

Now presenting a LUN to an AIX using LVM to format disk :

1 : let's say 300 Go and 100 Go are filled.

2 dedup is running and DataOntap says 50 % gain on that volume (meaning 250 Go are now Free at least on the NetApp side)

Result : AIX is still connect to a 300 Go LUN on which ONLY 200 Go are Free (where are those deduplicated 50 Go ??) This is what I observed so did I miss something ??

Thanks a lot.


adamfox Netapp Alumni

Larry can speak to this as well,  but that's how it works.  The space savings are seen on the controller side.  With NAS, controller space can equal client space (tree quotas can affect this, but let's leave that case out for now).  With SAN, the host doesn't see the controller space directly, it sees space in the filesystem inside the LUN.  The savings for that are virutalized to the point that the host can't detect it.  But you will see it with df or df -A on the controller and those space savings are real, i.e. you can use that space for different purposes.


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