From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josef Bacik Subject: Re: btrfs csum failed Date: Wed, 04 May 2011 10:39:52 -0400 Message-ID: <4DC16538.3070900@redhat.com> References: <4DC07A10.7070200@mur.at> <20110504002815.GA27861@dhcp231-156.rdu.redhat.com> <4DC0A153.3080806@mur.at> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linux-btrfs@vger.kernel.org To: Martin Schitter Return-path: In-Reply-To: <4DC0A153.3080806@mur.at> List-ID: On 05/03/2011 08:44 PM, Martin Schitter wrote: > Am 2011-05-04 02:28, schrieb Josef Bacik: >> Wait why are you running with btrfs in production? > > do you know a better alternative for continuous snapshots? :) > > it works surprisingly well since more than a year. > well the performance could be better for vm-image-hosting but it works. > > we used cache='writeback' for a long time but now all virtual instances > have set cache='none' > >> What OS is in this vm image? > > 2.6.30-bpo.1-amd64 with virtio-driver > > could you give me some advice how to debug/report this specific problem > more precise? > So there is a problem with DIO, since userspace can modify pages in flight we will end up with the wrong checksums since the data can change in flight. I was trying to come up with a way to fix this but there's really nothing to be done at the moment other than turn off checksumming per file. Windows was particularly bad about this, but I hadn't seen it with Linux guests (even though it should still be happening). So I'll come up with something to turn off checksumming per file to get around this for now, I'll try and get to that soonish. Thanks, Josef