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local-storage versus SAN sequential read performance comparison

From: Jan Nielsen <jan(dot)sture(dot)nielsen(at)gmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: local-storage versus SAN sequential read performance comparison
Date: 2012-05-21 14:17:36
Message-ID: CANxH4hHF8_qjiSoM5U_epPcRa2bu9N-wU8dArJOCQybYUxSV7w@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
This is outside of PG performance proper, but while testing pg_dump and
pg_restore performance on local-storage versus SAN storage I noticed a big
performance drops on in the SAN configuration. I'm told that both local
storage and SAN storage are 15k drives with local-storage running dual
RAID1 configuration while HP StorageWorks SB40c SAN is 10x15k RAID1+0.
Running a hdparm -tT tests with different read-ahead, I see the following
differences on /dev/sda (local-storage) and /dev/sdc (SAN storage). I'm
shocked at the drop in buffered disk read performance 150MB/sec versus
80MB/sec and surprised at the SAN variability at 1MB/sec versus 10MB/sec,
local-storage and SAN storage respectively.

For those who, unlike me, have experience looking at SAN storage
performance, is the drop in buffered disk reads and large variability the
expected cost of centralized remote storage in SANs with fiber-channel
communication, SAN fail-over, etc.

If you have any ideas or insights and/or if you know of a better suited
forum for this question I'd sure appreciate the feedback.


Cheers,

Jan

Attachment: readahead-sdc.png
Description: image/png (11.9 KB) (inlined above)
Attachment: readahead-sda.png
Description: image/png (12.2 KB) (inlined above)

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Next:From: Scott MarloweDate: 2012-05-21 15:41:12
Subject: Re: local-storage versus SAN sequential read performance comparison
Previous:From: Jan NielsenDate: 2012-05-19 19:11:49
Subject: Re: Configuration Recommendations

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