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Re: [dm-devel] [PATCH 26/30] ext4: do not send discards as barriers



On Tue 31-08-10 10:11:34, Tejun Heo wrote:
> On 08/30/2010 10:20 PM, Jan Kara wrote:
> >   My setup is that I have a dedicated partition / drive for a filesystem
> > which is written to from a guest kernel running under KVM. I have set it up
> > using virtio driver with cache=writeback so that the host caches the writes
> > in a similar way disk caches them. At some point I just kill the qemu-kvm
> > process and at that point I'd like to also throw away data cached by the
> > host...
> 
> $ echo 1 > /sys/block/sdX/device/delete
> $ echo - - - > /sys/class/scsi_host/hostX/scan
> 
> should do the trick.
  I've tested that when mounting with barrier=0 option inside KVM, this indeed
does destroy the filesystem rather badly. With the barrier option, ext4 has
already survived several crash cycles while running fsstress with
journal_async_commit option. So the patch seems to work as expected.

									Honza
-- 
Jan Kara <jack suse cz>
SUSE Labs, CR


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