On Mon, Mar 23, 2015 at 02:01:41PM -0600, Chris Murphy wrote: > I can't tell if this is a kvm virtio blk device regression, with > cache=none and cache=directsync, or if it's a Btrfs regression. > > The summary is that on a host using (Fedora) kernel 3.18.9, 3.19.2, or > any 4.0.0 kernel, with qcow2 on Btrfs, and either cache=none or > directsync, the guest Linux OS experiences many I/O blk device errors. > > https://bugzilla.redhat.com/show_bug.cgi?id=1204569 > > If I put the qcow2 on XFS, the problem doesn't happen. > > If I keep the qcow2 on Btrfs, and change the cache= to writeback, > writethrough, or unsafe, the problem doesn't happen. > > It happens with either qcow2 compat 0.10 or 1.1. Raw files were not > tested. And block devices other than virtio were not tested. > > In the guest, all file systems experience this and complain, some more > than others. Btrfs is most tolerant mainly reporting write errors but > completes an OS installation; ext4 complains a lot but also completes > an OS installation; XFS complains and eventually gives up with a > hardware I/O error and the OS installation fails. > > I did this test maybe two years ago and this combination was safe at that > time.
The last time we tracked down a similar problem, Josef found it was only on windows guests. Basically he tracked it down to buffers changing while in flight. I'll take a look. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
