From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: About SG Elements of request_buffer Date: Sun, 15 Oct 2006 11:40:16 -0400 Message-ID: <45325660.6070906@torque.net> References: <453223AA.50409@aboo.org> Reply-To: dougg@torque.net Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from pentafluge.infradead.org ([213.146.154.40]:23239 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S1751001AbWJOPiz (ORCPT ); Sun, 15 Oct 2006 11:38:55 -0400 In-Reply-To: <453223AA.50409@aboo.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Aboo Valappil Cc: linux-scsi@vger.kernel.org Aboo Valappil wrote: > Hi All, > > Thanks for all your support for my previous posts. > > I have two questions. > > 1. Is it safe to assume that all the SG elements of request_buffer are > page aligned? (Except the first one and last one), I mean, it is always > multiple of pages? > > 2. What are situations reading a scsi disk (using dd ) cause a write to > the disk? When I read my virtual scsi disk using dd command, block > layer is generating lot of SCSI write, as well as reads. Any thoughts? > Besides this observation, everything is working fine. Aboo, A comment on your second point: to bypass the vagaries of the block layer caching with dd (or sg_dd) use 'iflag=direct' and/or 'oflag=direct' as required. There may be alignment constraints. Doug Gilbert