On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote: > Alasdair G Kergon wrote: > > On Fri, Feb 15, 2008 at 01:08:21PM +0100, Andi Kleen wrote: > >> Implement barrier support for single device DM devices > > > > Thanks. We've got some (more-invasive) dm patches in the works that > > attempt to use flushing to emulate barriers where we can't just > > pass them down like that. > > I wonder if it's worth the effort to try to implement this. > > As far as I understand (*), if a filesystem realizes that the > underlying block device does not support barriers, it will > switch to using regular flushes instead No, typically the filesystems won't issue flushes, either. > - isn't it the same > thing as you're trying to do on an MD level? > > Note that a filesystem must understand barriers/flushes on > underlying block device, since many disk drives don't support > barriers anyway. > > (*) this is, in fact, an interesting question. I still can't > find complete information about this. For example, how safe > xfs is if barriers are not supported or turned off? Is it > "less safe" than with barriers? Will it use regular cache > flushes if barriers are not here? Try reading at the XFS FAQ: http://oss.sgi.com/projects/xfs/faq/#wcache Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
