RE: IO caching on xen?

["Dan Magenheimer" <dan.magenheimer@oracle.com>]

> marian klein, le Tue 15 Jul 2008 11:22:05 +0000, a écrit :
> > I am worried that the xen (or any other VM) with zvol 
> device from ZFS
> > (or any other file system.) may remove the benefits of ZFS,
> >  because the guest OS can write something to disk but the xen itself
> > can do some buffering
> > or lazy writing and it may delay to write to ZFS backend.
> 
> Xen doesn't do any kind of buffering or lazy writing.  It provides
> barriers to the guest, to ensure any needed coherency.
> 
> Samuel

I'm not sure if this is related or not...

I was party to some internal irc where it was believed
to be the case that when a file-backed vbd using file:'...'
is used, dom0's page cache may contain buffer pages that
may be inconsistent with the disk, whereas a file-backed
vbd using tap:aio:'...' does not suffer from the same problem.

Can someone confirm or deny (and if denied, was this fixed
recently)?

Thanks,
Dan