From owner-freebsd-scsi Fri Apr 7 8:56:57 2000 Delivered-To: freebsd-scsi@freebsd.org Received: from worf.qntm.com (worf.qntm.com [146.174.250.100]) by hub.freebsd.org (Postfix) with ESMTP id 684AC37BDB0 for ; Fri, 7 Apr 2000 08:56:55 -0700 (PDT) (envelope-from Stephen.Byan@quantum.com) Received: from mail3.qntm.com by worf.qntm.com with ESMTP (1.40.112.12/16.2) id AA167763010; Fri, 7 Apr 2000 08:56:50 -0700 Received: from milcmimb.qntm.com (milcmimb.qntm.com [146.174.18.77]) by mail3.qntm.com (8.8.6/8.8.6) with ESMTP id IAA21117; Fri, 7 Apr 2000 08:56:53 -0700 (PDT) Received: by milcmimb.qntm.com with Internet Mail Service (5.5.2650.10) id ; Fri, 7 Apr 2000 08:56:45 -0700 Message-Id: <8133266FE373D11190CD00805FA768BF02EE9F66@shrcmsg1.tdh.qntm.com> From: Stephen Byan To: "'Kenneth D. Merry'" , Stephen Byan Cc: freebsd-scsi@FreeBSD.ORG Subject: RE: newfs on IBM disks slower than Seagate disks? Date: Fri, 7 Apr 2000 08:56:13 -0700 Mime-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2650.10) Content-Type: text/plain; charset="iso-8859-1" Sender: owner-freebsd-scsi@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org Too bad. It'd be a useful thing for the I/O subsystem to know, both from a data integrity and from a performance viewpoint. In one of my former lives (at Hitachi), we hacked OSF/1's flavor of UFS to pass a "this is metadata" flag down to the disk device driver in the buf header. I arranged for the big honking mainframe disk controllers to put the unflagged writes in their copious volatile cache, and the flagged writes in their more-limited non-volatile cache. Regards, -Steve -----Original Message----- From: Kenneth D. Merry [mailto:ken@kdm.org] Sent: Friday, April 07, 2000 11:30 AM To: Stephen Byan Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: newfs on IBM disks slower than Seagate disks? On Fri, Apr 07, 2000 at 06:39:01 -0700, Stephen Byan wrote: > Does the FreeBSD SCSI subsystem set the FUA bit in the CDB for UFS metadata > writes? If so, then data integrity with WCE=1 is probably no worse than for > WCE=0, since the filesystem is caching non-metadata writes anyway. > > If UFS and CAM haven't made arrangements to hint which disk writes are > precious, then I think you're best off setting WCE=0, unless your system and > your disks are on a UPS. CAM doesn't set the FUA bit on metadata writes because it doesn't currently have a way to distinguish between metadata and normal data. Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message