From: | Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> |
---|---|
To: | pgsql-performance(at)postgresql(dot)org |
Cc: | tim(at)proximity(dot)com(dot)au, mstone+postgres(at)mathom(dot)us |
Subject: | Re: SAN performance mystery |
Date: | 2006-06-19 23:16:35 |
Message-ID: | 44973053.4080906@paradise.net.nz |
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Lists: | pgsql-performance |
Michael Stone wrote:
> On Mon, Jun 19, 2006 at 08:09:47PM +1000, Tim Allen wrote:
>> Certainly, the read performance of the SATA disk still beats the SAN,
>> and there is no way to lie about read performance.
>
> Sure there is: you have the data cached in system RAM. I find it real
> hard to believe that you can sustain 161MB/s off a single SATA disk.
>
Agreed - approx 60-70Mb/s seems to be the ballpark for modern SATA
drives, so get get 161Mb/s you would need about 3 of them striped
together (or a partially cached file as indicated).
What is interesting is that (presumably) the same test is getting such
uninspiring results on the SAN...
Having said that, I've been there too, about 4 years ago with a SAN that
had several 6 disk RAID5 arrays, and the best sequential *read*
performance we ever saw from them was about 50Mb/s. I recall trying to
get performance data from the vendor - only to be told that if we were
doing benchmarks - could they have our results when we were finished!
regards
Mark
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