On Oct 27, 2011, at 11:04 PM, Mark Wolek wrote:

> Still kicking around this idea and didn’t see it addressed in any of the 
> threads before the forum closed. 
> If one made an all ssd pool, would a log/cache drive just slow you down?  
> Would zil slow you down?

In general, a slog makes sense when the latency is significantly better than 
access to the main pool.
For an order of magnitude difference, it is a no brainer. For less significant 
differences, it can be debatable.

>  Thinking rotate MLC drives with sandforce controllers every few years to 
> avoid losing a drive to “sorry no more writes aloud” scenarios. 

Different SSDs have different performance behaviours.  If you don't pay 
attention to the details,
you might find your pool is faster than your slog :-)
 -- richard


ZFS and performance consulting
LISA '11, Boston, MA, December 4-9 

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