Data ONTAP Discussions

7.2.4 Deduplication on existing SnapMirror relationship

Got a customer who is using OSSV to backup to a netapp 2020 and then is replicating those volumes to another off site location. They have not yet enabled deduplication on the source volumes. What will be the impact if they enable deduplication on the sources with an already existing full size snapmirror relationship?

Thanks in advance for the assistance. I have my thoughts about how or what it will do but want to confirm before assisting the customer.


Re: 7.2.4 Deduplication on existing SnapMirror relationship

You can go ahead and start de-duplication on the source volume.

Make sure you have enough space on the source and good WAN bandwidth as after de-duplication finishes, A-SIS will generate a snapshot (depends on the size of the volume) which will be transferred to the destinatio site via VSM, same as your source filer snapshots.

After this transfer completes, you will see the destination volume showing as "snapmirrroed, online, sis".

After 1st de-duplication, run the same every quater (if the increamental changes are not large). Everytime, it will generate snapshot of A-SIS and the same will be replicated to the destination filer ans so on.

Re: 7.2.4 Deduplication on existing SnapMirror relationship

Are they using Volume SnapMirror or Qtree SnapMirror to replicate to the offsite system?  VSM should dedupe on both ends.  The initial run will generally result in bigger snapshots on both sides until the old snapshots rotate off.  With QSM, dedupe generally makes sense only on the destination as a post-process because data is 'rehydrated' during the transfer .  (I'm a bit fuzzy, but not sure if dedupe for QSM was supported in 7.2.4)

Re: 7.2.4 Deduplication on existing SnapMirror relationship

yes, deduplication for QSM is supported in 7.2.4. Deduplication doesn’t yield any network bandwidth savings as QSM works at the logical


Storage savings benefit at the QSM destination is achieved by running deduplication on the destination after QSM has finished transferring the data.