ONTAP Discussions

Deduplication on volume with a LUN


Greetings, everyone.


Deduplication increases storage efficiency. It works on blocks and can be enabled at volume level. If a volume contains a LUN, AFAIK the LUN and its underlying blocks are deduplicated as other blocks are, but in what way would a client treat a deduplicated LUN?


For example, a 100GB volume contains a 50GB LUN and deplication saving is 20%. That is, 50GB LUN actually accounts for 40GB physical blocks and the volume has 60GB available space. Assume the volume and the LUN are both thick-provisioned. Here come the questions:


Will the client see any difference before and after the volume is deduplicated? The LUN and its file system should remain the same, 50GB in this case, but will the client sees more available spaces after dedplication?


Any reply is very much appreciated. Thanks in advance.





The client calculates by it's own file system table that is unaware for the deduplication. the blocks allocated and used by the LUN never impacted by Dedup - these are virtual address that are a level above the block address used by the NetApp Volume level (where dedup take place).  


Having said that. some clients might use writesame command that will be translate to A-SIS (NetApp Dedup engine), i'm not aware for any OS that actually take user-visible counters based on that function, but this is the only source i can think of that a client can know anything about deduplication matrix.



Gidi Marcus (Linkedin) - Storage and Microsoft technologies consultant - Hydro IT LTD - UK