| From: | Greg Smith <greg(at)2ndquadrant(dot)com> |
|---|---|
| To: | Matthew Wakeling <matthew(at)flymine(dot)org> |
| Cc: | Yeb Havinga <yebhavinga(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Testing Sandforce SSD |
| Date: | 2010-07-26 15:28:02 |
| Message-ID: | 4C4DA982.5090308@2ndquadrant.com |
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| Lists: | pgsql-performance |
Matthew Wakeling wrote:
> Does your latency graph really have milliseconds as the y axis? If so,
> this device is really slow - some requests have a latency of more than
> a second!
Have you tried that yourself? If you generate one of those with
standard hard drives and a BBWC under Linux, I expect you'll discover
those latencies to be >5 seconds long. I recently saw >100 *seconds*
running a large pgbench test due to latency flushing things to disk, on
a system with 72GB of RAM. Takes a long time to flush >3GB of random
I/O out to disk when the kernel will happily cache that many writes
until checkpoint time.
--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us
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