ZFSv28 Dedup question

Freddie Cash fjwcash at gmail.com
Tue Jun 21 04:55:14 UTC 2011

On Mon, Jun 20, 2011 at 7:46 PM, James L. Lauser <james at jlauser.net> wrote:

> I have a (hopefully) simple question about ZFSv28 deduplication that is not
> very clearly answered in any of the documentation I've found.
> If I enable dedupe on a dataset, will newly written data dedupe against old
> data that was written before dedupe was enabled?  If not, is it worth
> forcing the data to be rewritten so that it makes it into the appropriate
> tables?
> No.  Dedupe only applies to newly written data.  The DDT (dedupe table)
only contains entries for data written after the "dedup" property is set on
a filesystem.

The only way to dedupe existing data is to copy/delete it, or "zfs send|zfs
recv" it, or otherwise re-write it.
Freddie Cash
fjwcash at gmail.com

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