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xen-devel
Re: [Xen-devel] AFS-based VBD backend
> > Q: Why not just use a loop device on top of AFS, with the 'file:'
> > VBD type?
> > A: Loop devices on top of AFS files hang with large volumes of
> > I/O -- looks like a deadlock of some sort (in my tests, a dd of
> > around 2-300 Mb into an AFS-based loop device appears to
> > consistently hang the kernel, even with a 500Mb or larger AFS
> > cache). In addition, an unmodified loop.c will not fsync() the
> > underlying file; changes won't get written back to the AFS server
> > until loop teardown. I've added an fsync() to the worker thread of
> > loop.c to take care of this every few seconds; that seems to work
> > but I can't really stress test it much because of the hang problem.
>
> That it's already possible to use normal files. :)
>
> So, no need for explicit support in xen. If your dom0 already knows and
> uses afs, just specify the file in the xen configuration:
>
> disk = [ 'file:/afs/file,sda1,w' ]
The OP did have an explanation why he didn't want to use a loop
device. However, I would say that the correct approach here is
probably to enhance/fix the existign loop support rather than adding a
whole new backend driver.
-- Keir
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