[OpenIndiana-discuss] ZFS with Dedupication for NFS server

Chris Ridd chrisridd at mac.com
Fri Apr 22 07:29:23 UTC 2011

On 21 Apr 2011, at 23:07, Toomas Soome wrote:

> the basic math behind the scenes is following (and not entirely determined):
> 1. DTT data is kept in metadata part of ARC; 
> 2. metadata default max is arc_c_max / 4. 
> note that you can rise that limit.
> 3. arc max is RAM - 1GB. 
> so, if you have 8GB of ram, your arc max is 7GB and max metadata is 1.75GB.  so, with server with 8GB of ram, your server will store MAX 1.75GB DTT in arc. the DTT entry is told to take 250B.

In this week's ZFS presentation at LOSUG, Darren Moffat suggested each DTT entry was 320 bytes. To get the number of entries needed, use zdb -DD poolname.

There's some good stuff in the ZFS Dedup FAQ <http://hub.opensolaris.org/bin/view/Community+Group+zfs/dedup>


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