[OpenIndiana-discuss] SSDs for ZFS Pool?

[Sašo Kiselkov]

On 08/20/2012 04:55 PM, Sebastian Gabler wrote:
> Hi,
> Questions:
> 
> - I understand that TRIM will not work in any stripe set, be it parity
> based or not, correct?

Correct, Illumos has no TRIM support (yet).

> - will heavy writes (such as transferring data from dumps, which will
> happen relatively often) lead to contention?

That's more a question of the quality of SATA drives you plan to
purchase. Read
http://gdamore.blogspot.com/2010/08/why-sas-sata-is-not-such-great-idea.html
for why SATA in a SAS environment isn't such a great idea. If you have
to use SATA, I recommend getting SAS interposers for them, e.g.
http://dataonstorage.com/dataon-products/6g-sas-to-sata-interposer-card-and-kit.html
(for example all SATA drives shipped in Sun JBODs had interposers)

> - Should I upgrade the HBAs to something newer like LSI2008, for
> compatibility reasons (no, I probably don't need the extra bandwidth SAS
> 6g offers!)

The LSI SAS1068 are very high quality chips, so if you feel you don't
need 6G SAS, there's probably no need to upgrade. LSI SAS2008, however,
can be had at extremely competitive prices (<100USD for a new
Dell-branded external HBA card with the chips is an extremely attractive
proposition) and are also very stable.

> - Are there any SSDs that you could recommend?

OCZ Talos R, though these are quite pricey. You might want to look into
stuffing it with normal 7k2 rpm drives and getting a suitably-large
L2ARC device (these can do wonders, my crappy little 60GB Vertex 3 can
push >90MB/s and >10k iops in 8k random reads).

> - with some desktop HDs, I experienced that they will be kicked out of
> the array for no obvious reason - does that happen with consumer SSDs as
> well, i.e. while the controller re-balances free cells for writing?

It's more a problem of the SATA circuitry which can't cope with the
constant battery of commands when your pool is taking a bad beating. See
above for my opinion on SATA vs. SAS.

> - should I better use 10 K SAS drives w/ flash-based ZIL?

Drive speed isn't all that important if you get a suitably large L2ARC.
If your databases are going to be used for testing only (so data loss in
case the machine goes down isn't that big an issue), you might want to
turn the ZIL entirely off. It's quite a performance killer unless you
choose to dump a bunch of money into an expensive slog device (e.g.
ddrdrive, zeusram, etc.).

--
Saso