From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: scsi write barriers (ordered tags)? Date: 05 Feb 2003 14:24:49 -0600 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <1044476691.1775.72.camel@mulgrave> References: <200302051809.NAA23237@orville.steeleye.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: (from root@localhost) by pogo.mtv1.steeleye.com (8.9.3/8.9.3) id MAA28611 for ; Wed, 5 Feb 2003 12:24:54 -0800 In-Reply-To: <200302051809.NAA23237@orville.steeleye.com> List-Id: linux-scsi@vger.kernel.org To: jordan.breeding@attbi.com Cc: SCSI Mailing List On Wed, 2003-02-05 at 11:58, jordan.breeding@attbi.com wrote: > I understand that SCSI drives and controllers are much more complicated than their IDE counterparts and that to implement ordered tags in SCSI is more complicated. However, doesn't FreeBSD's CAM layer have some kind of implementation of this which makes it safe to use soft-updates and write back cache together? Actually, no. The problem that caches cause is that they cache data, not transactions. You can force the caches to respect transaction order by flushing them, but that gets expensive. I thought that I read that sometime ago but I have been trying to find references to it on google this morning and couldn't find any. I guess what I am really after is to fold: 1) Will Linux's SCSI layer get modified at _any_ point to support something like this to benefit ext3/reiserfs/xfs/jfs? 2) If this will be attempted at some point will it be later in 2.5/2.6 or will this definitely be 2.7/2.8 material? Thanks for the info and the response. Like I said, the infrastructure exists. There's no compelling reason to enable it (mainly because most of the benchmarks say it causes a slowdown). James