Erik Trimble <erik.trim...@oracle.com> wrote:
> On 7/25/2011 3:32 AM, Orvar Korvar wrote:
> > How long have you been using a SSD? Do you see any performance decrease? I
> > mean, ZFS does not support TRIM, so I wonder about long term effects...
>
> Frankly, for the kind of use that ZFS puts on a SSD, TRIM makes no
> impact whatsoever.
>
> TRIM is primarily useful for low-volume changes - that is, for a
> filesystem that generally has few deletes over time (i.e. rate of change
> is low).
>
> Using a SSD as a ZIL or L2ARC device puts a very high write load on the
> device (even as an L2ARC, there is a considerably higher write load than
> a "typical" filesystem use). SSDs in such a configuration can't really
> make use of TRIM, and depend on the internal SSD controller block
> re-allocation algorithms to improve block layout.
>
> Now, if you're using the SSD as primary media (i.e. in place of a Hard
> Drive), there is a possibility that TRIM could help. I honestly can't
> be sure that it would help, however, as ZFS's Copy-on-Write nature means
> that it tends to write entire pages of blocks, rather than just small
> blocks. Which is fine from the SSD's standpoint.
Writing to an SSD is: clear + write + verify
As the SSD cannot know that the rewritten blocks have been unused for a while,
the SSD cannot handle the clear operation at a time when there is no interest
in the block, the TRIM command is needed to give this knowledge to the SSD.
Jörg
--
EMail:jo...@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
j...@cs.tu-berlin.de (uni)
joerg.schill...@fokus.fraunhofer.de (work) Blog:
http://schily.blogspot.com/
URL: http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
