ZFSv28 Dedup question

James L. Lauser james at jlauser.net
Tue Jun 21 12:32:58 UTC 2011

Thanks for the info.  This is what I suspected, but just wanted to verify.

Given this, then the 1.11x ratio shown for dedup in 'zpool list' means that
of the data that was written since dedup was enabled, it deduped at a ratio
of 1.11:1?

--  James L. Lauser
    james at jlauser.net

On Tue, Jun 21, 2011 at 12:55 AM, Freddie Cash <fjwcash at gmail.com> wrote:

> 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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