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 david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
