On 2018-06-15 13:40, Chris Murphy wrote:
On Fri, Jun 15, 2018 at 5:33 AM, ein <ein....@gmail.com> wrote:
Hello group,
does anyone have had any luck with hosting qemu kvm images resided on BTRFS
filesystem while serving
the volume via iSCSI?
I encouraged some unidentified problem and I am able to replicate it. Basically
the NTFS filesystem
inside RAW image gets corrupted every time when Windows guest boots. What is
weired is that changing
filesystem for ext4 or xfs solves the issue.
The problem replication looks as follows:
1) run chkdsk on the guest to make sure the filesystem structure is in good
shape,
2) shut down the VM via libvirtd,
3) rsync changes between source and backup image,
4) generate SHA1 for backup and original and compare it,
5) try to run guest on the backup image, I was able to boot windows once for
ten times, every time
after reboot NTFS' chkdsk finds problems with filesystem and the VM is unable
to boot again.
What am I missing?
VM disk config:
<disk type='file' device='disk'>
<driver name='qemu' type='raw' cache='none' io='native'/>
cache=none uses O_DIRECT, and that's the source of the issue with VM
images on Btrfs. Details are in the list archive.
I'm not really sure what you want to use with Windows in this
particular case, probably not cache=unsafe though. I'd say give
writethrough a shot and see how it affects performance and fixes this
problem.
cache=writethrough is probably going to be the best option, unless you
want to switch to cache=writeback and disable write caching in Windows
(which from what I hear can actually give better performance than using
cache=none).
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