[Beowulf] SSD caching for parallel filesystems

Bill Broadley bill at cse.ucdavis.edu
Sat Feb 9 13:32:34 PST 2013


On 02/09/2013 01:22 PM, Vincent Diepeveen wrote:
> SATA is very bad protocol for SSD's.
> 
> SSD's allows perfectly parallel stores and writes, SATA doesn't.
> So SATA really limits the SSD's true performance.

SSDs and controllers often support NCQ which allows multiple outstanding
requests.  Not sure if that fits the definition of "perfectly parallel",
but it does allow for outstanding requests to be answered in the order
of the devices choosing.

In fact the higher IOP rates would be impossible without it.  Note how
the latency for a single IOP is much higher than peak 1 second / (peak
IOPs).




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