> -----Original Message----- > From: linux-btrfs-ow...@vger.kernel.org [mailto:linux-btrfs- > ow...@vger.kernel.org] On Behalf Of Chris Murphy > Sent: Wednesday, 25 March 2015 3:10 AM > To: Chris Mason; Chris Murphy; Btrfs BTRFS > Subject: Re: kvm bug, guest I/O blk device errors when qcow2 backing file is > on Btrfs > > On Mon, Mar 23, 2015 at 3:13 PM, Chris Mason <c...@fb.com> wrote:
> > 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. > > Looks like cache=none and directsync share O_DIRECT in common. > > This patch suggests neither of those cache options should be used (for > different reasons). > https://github.com/libguestfs/libguestfs/commit/749e947bb0103f19feda0f2 > 9b6cbbf3cbfa350da > > I stumbled on this testing GNOME Boxes which is using cache=none, which it > probably shouldn't, but nevertheless none and directsync also shouldn't > cause problems on Btrfs. I've got a Windows 2012 guest VM running on a linux host and I also have trouble with cache=none. There is one particular inode on the BTRFS filesystem that gets csum errors about every 6-18 hours. I swapped just about everything (hardware) trying to find the problem, but then I remembered I was experimenting with cache options. I changed it back to default and the problem went away. Interrestingly there are no reported errors on the VM. Paul.
