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Re: [Xen-devel] AFS-based VBD backend

On Thu, Dec 23, 2004 at 10:37:17AM +0000, Luciano Miguel Ferreira Rocha wrote:
> On Thu, Dec 23, 2004 at 12:55:58AM -0800, Steve Traugott wrote:
> > 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.

> > What did I miss?  ;-)
> 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' ]

Already covered in the above FAQ answer.  ;-)  The 'file:...' VBD type
just uses the loop device driver underneath.  Won't work on top of AFS.

Stephen G. Traugott  (KG6HDQ)
UNIX/Linux Infrastructure Architect, TerraLuna LLC
http://www.stevegt.com -- http://Infrastructures.Org

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