[oi-dev] SSD-based pools

[Bayard Bell]

General warning: have a look at power safety issues before building all-SSD
pools. Unless the drive is power-safe, you may find that writes
acknowledged by the controller that are meant to be flushed aren't. There's
been a reasonable amount of research, published on this, including one
paper by Luke Kenneth Casson Leighton and another supported by HP presented
at FAST, and the general conclusion is that consumer SSDs don't get this
right. Intel had some models that did this, but these features now appear
to be exclusive to their data center products. Hitachi does not claim that
the 850s are power safe, so they are only suitable for L2ARC.

Have you had a look at FMA telemetry for the devices?

Cheers,
Bayard

On 25 September 2014 23:46, Andrew M. Hettinger <AHettinger at prominic.net>
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?
>
>   pool: test-array
>  state: DEGRADED
> status: One or more devices has experienced an unrecoverable error.  An
>         attempt was made to correct the error.  Applications are
> unaffected.
> action: Determine if the device needs to be replaced, and clear the errors
>         using 'zpool clear' or replace the device with 'zpool replace'.
>    see: http://illumos.org/msg/ZFS-8000-9P
>   scan: scrub repaired 0 in 0h0m with 0 errors on Wed Sep 24 18:20:56 2014
> config:
>
>         NAME                       STATE     READ WRITE CKSUM
>         test-array                 DEGRADED     0     0     0
>           mirror-0                 DEGRADED     0     0     0
>             c0t50025388700060D4d0  DEGRADED     0     0   155  too many
> errors
>             c0t50025388700060AEd0  DEGRADED     0     0   149  too many
> errors
>             c0t50025388700060C2d0  DEGRADED     0     0   174  too many
> errors
>         logs
>           c0t50025388A067DBE9d0    ONLINE       0     0     0
>
> errors: No known data errors
>   ---- errors ---
>   s/w h/w trn tot device
>     0   2   6   8 c0t50025388700060D4d0
>     0   0   0   0 c0t50025388700060AEd0
>     0   0   0   0 c0t50025388700060C2d0
>     0   0   0   0 c0t50025388A067DBE9d0
>
>
> Andrew Hettinger
> http://Prominic.NET | Skype: AndrewProminic
> Tel: 866.339.3169 (toll free) -or- 1.217.356.2888 x. 110 (int'l)
> Fax: 866.372.3356 (toll free) -or- 1.217.356.3356            (int'l)
>
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>
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