From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:36732) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QCqC1-0000m0-HG for qemu-devel@nongnu.org; Thu, 21 Apr 2011 05:28:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QCqC0-00066I-Cg for qemu-devel@nongnu.org; Thu, 21 Apr 2011 05:28:57 -0400 Received: from mail-vx0-f173.google.com ([209.85.220.173]:64747) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QCqC0-00066C-A3 for qemu-devel@nongnu.org; Thu, 21 Apr 2011 05:28:56 -0400 Received: by vxb41 with SMTP id 41so1289249vxb.4 for ; Thu, 21 Apr 2011 02:28:55 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110421090935.GA5381@lst.de> References: <1303375391-26679-1-git-send-email-ronniesahlberg@gmail.com> <20110421085026.GA4817@lst.de> <20110421090935.GA5381@lst.de> Date: Thu, 21 Apr 2011 19:28:55 +1000 Message-ID: From: ronnie sahlberg Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] iSCSI support for QEMU List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: qemu-devel@nongnu.org, stefanha@linux.vnet.ibm.com On Thu, Apr 21, 2011 at 7:09 PM, Christoph Hellwig wrote: >> 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=3D0 by defa= ult. > Now if you target has WCE=3D1 it will cache data internally, and your > iscsi initiator will never flush it out to disk. My target does not do any caching at all. It happily ignores both FUA and FUA_NV bits and always destage all data to stable storage before sending SCSI_STATUS_GOOD back to the initiator. I use the same target and the same LUN and the same settings for both testi= ng QEMU+openiscsi-mounted-lun and QEMU+libiscsi I do not understand why my target would have data integrity problem when used with libiscsi but not with open-iscsi mounted lun? > > We only claim WCE=3D1 to the guest if cache=3Dwriteback or cache=3Dnone a= re > set. =A0So ignoring the issue of having a cache on the initiator side > you must implement stable writes for the default cache=3Dwritethrough > 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. My target right now does such flushes for writes. I fail to see why FUA, FUA_NV or flushes have any relevance to a test that just involves reading data off the lun. I think this discussion is strange. I would like discussion about the merits of my patch and if features like built-in iscsi support that enterprise users find useful are desireable in QEMU. I do not find discussions about semantics of my particular iscsi target to be meaningful for that purpose. regards ronnie sahlberg