On Jul 5, 2009, at 7:47 PM, Richard Elling <richard.ell...@gmail.com>
wrote:
Ross Walker wrote:
On Jul 5, 2009, at 6:06 AM, James Lever <j...@jamver.id.au> wrote:
On 04/07/2009, at 3:08 AM, Bob Friesenhahn wrote:
It seems like you may have selected the wrong SSD product to use.
There seems to be a huge variation in performance (and cost) with
so-called "enterprise" SSDs. SSDs with capacitor-backed write
caches seem to be fastest.
Do you have any methods to "correctly" measure the performance of
an SSD for the purpose of a slog and any information on others
(other than anecdotal evidence)?
There are two types of SSD drives on the market, the fast write SLC
(single level cell) and the slow write MLC (multi level cell). MLC
is usually used in laptops as SLC drives over 16GB usually go for
$1000+ which isn't cost effective in a laptop. MLC is good for read
caching though and most use it for L2ARC.
Please don't classify them as MLC vs SLC or you'll find yourself
totally
confused by the modern MLC designs which use SLC as a cache. Be
happy with specs: random write iops: slow or fast.
Thanks for the info. SSD is still very much a moving target.
I worry about SSD drives long term reliability. If I mirror two of
the same drives what do you think the probability of a double failure
will be in 3, 4, 5 years?
What I would really like to see is zpool's ability to fail-back to an
inline zil in the event an external one fails or is missing. Then one
can remove an slog from a pool and add a different one if necessary or
just remove it altogether.
-Ross
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