From mboxrd@z Thu Jan 1 00:00:00 1970 From: Patrick Mansfield Subject: Re: Perform uncached reads on SCSI drives? Date: Thu, 21 Apr 2005 09:14:21 -0700 Message-ID: <20050421161421.GA20143@us.ibm.com> References: <66F9227F7417874C8DB3CEB0577274170450EE@MILEX0.Miltope.local> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e33.co.us.ibm.com ([32.97.110.131]:31925 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S261503AbVDUQOe (ORCPT ); Thu, 21 Apr 2005 12:14:34 -0400 Received: from d01relay02.pok.ibm.com (d01relay02.pok.ibm.com [9.56.227.234]) by e33.co.us.ibm.com (8.12.10/8.12.9) with ESMTP id j3LGEW4I140844 for ; Thu, 21 Apr 2005 12:14:33 -0400 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay02.pok.ibm.com (8.12.10/NCO/VER6.6) with ESMTP id j3LGEWax050224 for ; Thu, 21 Apr 2005 12:14:32 -0400 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.12.11/8.12.11) with ESMTP id j3LGEWd3027531 for ; Thu, 21 Apr 2005 11:14:32 -0500 Content-Disposition: inline In-Reply-To: <66F9227F7417874C8DB3CEB0577274170450EE@MILEX0.Miltope.local> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Drew Winstel Cc: "Linux-scsi (E-mail)" 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