[ZFS] Using SSD with partitions

[Alexander Leidinger]

On Sun, 16 Oct 2011 00:45:50 -0400 Patrick Donnelly
<batrick at batbytes.com> wrote:


> Hi list,
> 
> I've got an array for home use where my boot drive (UFS) finally died.
> I've decided to upgrade to a SSD for a replacement but am looking to
> maybe simultaneously improving performance of my ZFS array. Naturally

What do you mean by "array"? How many disks and which type (HD or SSD)?
Which pool configuration you are aiming at?

> a FreeBSD install doesn't use much space so partitioning the drive to
> get maximum usage seems wise. I was thinking for a hypothetical 40GB
> drive:
> 
> 20GB -- FreeBSD / partition
> 2GB  -- ZFS ZIL
> 18GB -- ZFS Cache
> 
> What I'm wondering is if this will be a bad idea. I know that SSDs are
> not designed to be written to *a lot*, which a ZIL will experience. Is
> this a bad idea? I'm hoping for experiences from people in similar
> scenarios. As I'm not an enterprise IT person who can't simply choose
> to just throw more mon-- I mean SSDs -- at the problem, I need to be
> efficient. :) [I'm thinking the cache drive partition might be
> pointless as I don't think I'd benefit that much from it.]

ZIL and cache shall be on devices which are faster than the rest of the
pool (exception for an edge case: saturated I/O-path to the main
pool-disks, not saturated I/O-path to the ZIL/cache, and data in cache
or targeted for the ZIL).

If your ZIL/cache partitions on SSD are aimed for a pool which consists
of normal HD's, go for it. If you have only SSDs (or only one single
disk in total), it is most probably better (surely for a desktop system)
to keep it simple (no ZIL/cache partitions).

Bye,
Alexander.

-- 
http://www.Leidinger.net    Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org       netchild @ FreeBSD.org  : PGP ID = 72077137