From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:33738) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QCptJ-0006UU-TW for qemu-devel@nongnu.org; Thu, 21 Apr 2011 05:09:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QCptJ-0002jk-1N for qemu-devel@nongnu.org; Thu, 21 Apr 2011 05:09:37 -0400 Received: from verein.lst.de ([213.95.11.211]:46693 helo=newverein.lst.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QCptI-0002jb-Px for qemu-devel@nongnu.org; Thu, 21 Apr 2011 05:09:36 -0400 Date: Thu, 21 Apr 2011 11:09:35 +0200 From: Christoph Hellwig Message-ID: <20110421090935.GA5381@lst.de> References: <1303375391-26679-1-git-send-email-ronniesahlberg@gmail.com> <20110421085026.GA4817@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] iSCSI support for QEMU List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: ronnie sahlberg Cc: Christoph Hellwig , stefanha@linux.vnet.ibm.com, qemu-devel@nongnu.org > In my patch, there are NO data integrity issues. > Data is sent out on the wire immediately as the guest issues the write. > Once the guest issues a flush call, the flush call will not terminate > until the SYNCCACHE10 task has completed. No guest will even issue a cache flush, as we claim to be WCE=0 by default. Now if you target has WCE=1 it will cache data internally, and your iscsi initiator will never flush it out to disk. We only claim WCE=1 to the guest if cache=writeback or cache=none are set. So ignoring the issue of having a cache on the initiator side you must implement stable writes for the default cache=writethrough behaviour by either seeting the FUA bit on your writes, or doing a cache flush after every write in case the target does not support FUA.