[Qemu-devel] Re: Notes on block I/O data integrity

[Christoph Hellwig]

On Tue, Aug 25, 2009 at 02:33:30PM -0500, Javier Guerra wrote:
> On Tue, Aug 25, 2009 at 1:11 PM, Christoph Hellwig<address@hidden> wrote:
> > ??- barrier requests and cache flushes are supported by all local
> > ?? disk filesystem in popular use (btrfs, ext3, ext4, reiserfs, XFS).
> > ?? However unlike the other filesystems ext3 does _NOT_ enable barriers
> > ?? and cache flush requests by default.
> 
> what about LVM? iv'e read somewhere that it used to just eat barriers
> used by XFS, making it less safe than simple partitions.

Oh, any additional layers open another by cans of worms.  On Linux until
very recently using LVM or software raid means only disabled
write caches are safe.