[illumos-Developer] Dedup

[Garrett D'Amore]

If you mean, does dedup still need a bunch of system memory *or* an SSD backed L2ARC (and a still large, although possibly smaller system memory size), then the answer is *yes*.  The DDT still wants to live in the ARC, and you really don't want to have to go to spinning rust to access it.

There are many considerations when enabling dedup, and in general, you should be very careful before you enable it.  If you are going to only reduce your storage requirements by half or less, then I would not use it at all.  And I would never use it unless I had a boatload of memory to begin with.  (One possible exception would be if my entire data set was located on SSDs.  In that case, dedup even with a lower dedup ratio might still make sense, given the precious nature of bytes located on SSD.)

  -- Garrett D'Amore

On Jul 18, 2011, at 8:12 AM, "Marcelo Leal" <sunos.x86 at gmail.com> wrote:

> Hello there,
> I was reading this (old) post from Roch:
> 
> http://blogs.oracle.com/roch/entry/dedup_performance_considerations1
> 
> And looking at the comment, that is still true for the actual
> implementaion of dedup on ZFS?
> I mean, the performance enhancement from deduped block on memory, i
> think can be better than the space utilization on disk. ;-)
> So, i'm asking if that drawback persists on the updated code today.
> 
> Thanks!
> 
> Leal
> [ http://www.eall.com.br/blog ]
> -------=- pOSix rules -=-------
> 
> _______________________________________________
> Developer mailing list
> Developer at lists.illumos.org
> http://lists.illumos.org/m/listinfo/developer