[oi-dev] SSD-based pools

[Schweiss, Chip]

> On 26/09/2014 00:46, Andrew M. Hettinger wrote:
>>
>>> I'm presently running tests on a pool using 3x Samsung 850 SSDs on a
>>> LSI-9211-8i
>>> (IT) contoller. I thought I'd try seperating the intent log to see if
>>> lowering
>>> the write amplification on the pool-drives would help, so I added another
>>> matching SSD for that, but under load I still seem to get extensive
>>> checksum
>>> errors. Does anyone have any ideas as to what would be causing this?
>>>
>>>
>>
> I would suspect hardware.   Avoid overly cheap SAS cables.

I run nearly 100 SSDs with Illumos based ZFS.  63 of them are Samsung 840
Pros in a pure SSD pool in a Supermicro JBOD.   I don't see any checksum
problems.

The 850 has the same firmware as the 840 so the new generation should not
make any difference.

I also always run SAS to SATA interposers to keep the SAS buses happy.
However, Samsung SSDs are the only brand SSD that I found to consistently
work with the interposers.

All my HBAs are LSI 2308 and 2008 controller based.   Make sure your
firmware is up to date.  There have been many SSD related fixes in the LSI
HBA.

If you can avoid it don't use a SAS expander, they will slow things down
and without interposers are susceptible to reset storms.

A log device is really necessary on an SSD pool.   The sync write behavior
of ZFS simply does not work well with SSDs with out a log.   Using an 850
is not a good choice for a log device because it does not have power loss
protections. You are better off turning sync off than trying to use them as
a log.

-Chip
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