linux-kernel - Different buffered IO performance with SCSI and SATA with same unbuffered performance

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Date:	Mon, 16 Mar 2009 22:23:59 +0100
From:	Pedro Larroy <pedro.larroy.lists@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Different buffered IO performance with SCSI and SATA with same 
	unbuffered performance

Hello. I'm puzzled about these measures with one U2W/160 SCSI disk and
a WD raptor SATA.
kernel is 2.6.28.7
This measures are on the same box, notice the very low rate of
buffered with the sata drive.

sata drive:
hdparm -t /dev/sdb
Timing buffered disk reads:   54 MB in  3.04 seconds =  17.78 MB/sec
hdparm --direct -t /dev/sdb
Timing O_DIRECT disk reads:  178 MB in  3.03 seconds =  58.67 MB/sec

scsi drive:
hdparm -t /dev/sda
Timing buffered disk reads:  200 MB in  3.03 seconds =  66.10 MB/sec
hdparm --direct -t /dev/sda
Timing O_DIRECT disk reads:  200 MB in  3.02 seconds =  66.14 MB/sec

Is this ok?

Regards. Pedro.

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