From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Re: [PATCH 26/30] ext4: do not send discards as barriers Date: Mon, 30 Aug 2010 17:24:53 -0300 Message-ID: <4C7C1395.5020000@redhat.com> References: <1282751267-3530-1-git-send-email-tj@kernel.org> <1282751267-3530-27-git-send-email-tj@kernel.org> <20100825155842.GA3229@lst.de> <20100825160032.GC3229@lst.de> <4C753D75.2010305@kernel.org> <20100825200223.GE2738@quack.suse.cz> <4C76250B.6060800@kernel.org> <20100827173147.GA12374@quack.suse.cz> <20100830202034.GB12226@quack.quadriga.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100830202034.GB12226@quack.quadriga.com> Sender: linux-raid-owner@vger.kernel.org To: Jan Kara Cc: Jeff Moyer , Tejun Heo , Christoph Hellwig , jaxboe@fusionio.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, linux-raid@vger.kernel.org, James.Bottomley@suse.de, tytso@mit.edu, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp, dm-devel@redhat.com, vst@vlnb.net, hare@suse.de, neilb@suse.de, rusty@rustcorp.com.au, mst@redhat.com, jeremy@goop.org, snitzer@redhat.com, k-ueda@ct.jp.nec.com, Christoph Hellwig List-Id: linux-raid.ids On 08/30/2010 05:20 PM, Jan Kara wrote: > On Mon 30-08-10 15:56:43, Jeff Moyer wrote: >> Jan Kara writes: >> >>> An update: I've set up an ext4 barrier testing in KVM - run fsstress, >>> kill KVM at some random moment and check that the filesystem is consistent >>> (kvm is run in cache=writeback mode to simulate disk cache). About 70 runs >> But doesn't your "disk cache" survive the "power cycle" of your guest? > Yes, you're right. Thinking about it now the test setup was wrong because > it didn't refuse writes to the VM's data partition after the moment I > killed KVM. Thanks for catching this. I will probably have to use the fault > injection on the host to disallow writing the device at a certain moment. > Or does somebody have a better option? > My setup is that I have a dedicated partition / drive for a filesystem > which is written to from a guest kernel running under KVM. I have set it up > using virtio driver with cache=writeback so that the host caches the writes > in a similar way disk caches them. At some point I just kill the qemu-kvm > process and at that point I'd like to also throw away data cached by the > host... > > Honza Hi Jan, Not sure if this is relevant, but what we have been using for part of the testing is an external e-sata enclosure that you can stick pretty much any S-ATA disk into. Important to drop power to the external disk (do not pull the s-ata cable, the firmware will destage the write cache for some/many disks if it has power and sees link loss :)). Once you turn the drive back on, the test was can you mount without error, unmount and do a fsck -f to verify no meta-data corruption, Ric