topic Re: vol copy and deduplication in ONTAP Discussions

vol copy and deduplication

benknights — Thu, 05 Jun 2025 07:13:32 GMT

One of my customers is looking to perform some data migrations. These will be within the same filer. The question they have is as follows:

‘If the source volume has 500GB of dedupe savings, should I account for this when I create the new destination volume, i.e. add an additional 500GB of space on top of the used space requirements? I will enable dedupe on the destination volume once the data has been migrated but initially I am assuming that we'll lose the dedupe savings.’

They intend to use ‘vol copy’ as they want to copy over their snapshots as well as the data.

Thanks,

Ben.

Re: vol copy and deduplication

RichardSopp — Mon, 14 Jun 2010 19:42:35 GMT

Ben,

Having just performed 100 vol copy migrations on a lab system with dedupe enabled volumes here’s a few answers based on firsthand experience.

Destination volume was the almost the same size (+1%) as the source volume (some copies failed first time as the destination volume seems to need a little more free space – probably for the snapshot created by the vol copy operation).

Vol copy process maintains the de-duped state of the source volume on the destination volume so no need to run sis start –s on destination volume

Vol copy process maintains the de-dupe scheduling of the source volume on the destination volume so no need to run sis config on destination volume

Hope this helps

Richard

Re: vol copy and deduplication

benknights — Mon, 14 Jun 2010 20:29:47 GMT

Richard,

That's great. Thanks for the quick reply.

Ben.

Re: vol copy and deduplication

calvarez — Tue, 15 Jun 2010 07:23:05 GMT

Remember, starting with Data ONTAP 7.3, some of the deduplication metadata

files do not get copied by the vol copy command, because they are located

outside of the volume in the aggregate. The data will indeed retain the

space savings, and the deduplication process will continue for any new data

written to the destination volume. The deduplication process obtains space

savings for the new data only and does not deduplicate between the new data

and the pre-existing (copied) data. To run deduplication for all the data in

the cloned volume (and thus obtain higher space savings), use the sis start

-s command.