From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Some very basic questions Date: Wed, 22 Oct 2008 20:32:26 +0200 Message-ID: <48FF71BA.8040206@redhat.com> References: <20081021132322.271ad728.skraw@ithnet.com> <1224597580.27474.93.camel@think.oraclecorp.com> <1224622451.7412.1.camel@telesto> <48FE553D.80501@redhat.com> <1224642544.7189.17.camel@telesto> <48FF038A.4010105@redhat.com> <48FF0625.6040400@kernel.org> <48FF2343.3070107@redhat.com> <48FF276B.6090602@kernel.org> <48FF296F.9060009@redhat.com> <48FF515B.2030209@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Ric Wheeler , Eric Anopolsky , Chris Mason , Stephan von Krawczynski , linux-btrfs@vger.kernel.org To: Tejun Heo Return-path: In-Reply-To: <48FF515B.2030209@kernel.org> List-ID: Tejun Heo wrote: > For most SATA drives, disabling write back cache seems to take high > toll on write throughput. :-( > > I measured this yesterday. This is true for pure write workloads; for mixed read/write workloads the throughput decrease is negligible. > As long as the error status is sticky, it doesn't have to hold on to > the data, it's not gonna be able to write it anyway. The drive has to > hold onto the failure information only. Yeah, but fully agreed on > that it's most likely dependent on the specific firmware. There isn't > any requirement on how to handle write back failure in the ATA spec. > It wouldn't be too surprising if there are some drives which happily > report the old data after silent write failure followed by flush and > power loss at the right timing. I got flamed for this on another list, but let's disable the write cache and live with the performance drop. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.