On Thu, Mar 31, 2016 at 09:25:33PM -0600, Jens Axboe wrote:
> On 03/31/2016 06:46 PM, Dave Chinner wrote:
> >>>virtio in guest, XFS direct IO -> no-op -> scsi in host.
> >>
> >>That has write back caching enabled on the guest, correct?
> >
> >No. It uses virtio,cache=none (that's the "XFS Direct IO" bit above).
> >Sorry for not being clear about that.
>
> That's fine, it's one less worry if that's not the case. So if you
> cat the 'write_cache' file in the virtioblk sysfs block queue/
> directory, it says 'write through'? Just want to confirm that we got
> that propagated correctly.
No such file. But I did find:
$ cat /sys/block/vdc/cache_type
write back
Which is what I'd expect it to safe given the man page description
of cache=none:
Note that this is considered a writeback mode and the guest
OS must handle the disk write cache correctly in order to
avoid data corruption on host crashes.
To make it say "write through" I need to use cache=directsync, but
I have no need for such integrity guarantees on a volatile test
device...
Cheers,
Dave.
--
Dave Chinner
da...@fromorbit.com
