From: Patrick Mansfield <patmans@us.ibm.com>
To: Drew Winstel <DWinstel@Miltope.com>
Cc: "Linux-scsi (E-mail)" <linux-scsi@vger.kernel.org>
Subject: Re: Perform uncached reads on SCSI drives?
Date: Thu, 21 Apr 2005 09:14:21 -0700 [thread overview]
Message-ID: <20050421161421.GA20143@us.ibm.com> (raw)
In-Reply-To: <66F9227F7417874C8DB3CEB0577274170450EE@MILEX0.Miltope.local>
On Thu, Apr 21, 2005 at 10:44:23AM -0500, Drew Winstel wrote:
> It has been a busy week, I know, but does anyone have any tips?
You could try setting read cache disable, I don't know if that setting
must be honored, or how ATA/SATA handle it. See mode page 8 for SCSI block
commands.
The sg utilities sg_modes can probably set it.
Better yet, do IO to more locations on the disk, not just the very
beginning and the very end.
> The reads we're calling are getting cached. If we call 100 reads--50 to the
> beginning of the drive alternating with 50 to the end--the first read will
> sometimes appear to have a realistic result, then the rest will all complete
> in the neighborhood of 10 microseconds.
-- Patrick Mansfield
next prev parent reply other threads:[~2005-04-21 16:14 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-04-21 15:44 Perform uncached reads on SCSI drives? Drew Winstel
2005-04-21 16:14 ` Patrick Mansfield [this message]
-- strict thread matches above, loose matches on Subject: below --
2005-04-21 21:41 Drew Winstel
2005-05-20 12:16 ` Douglas Gilbert
2005-04-13 13:02 Drew Winstel
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