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RE: [Xen-devel] questions about production use

To: "Nick Craig-Wood" <ncw1@xxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] questions about production use
From: "Williamson, Mark A" <mark.a.williamson@xxxxxxxxx>
Date: Fri, 23 Jan 2004 20:26:15 -0000
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Thread-topic: [Xen-devel] questions about production use
> If Xen could run using files that would be most interesting to us - it
> would mean the minimum change to our current setup.

Currently, it's not possible to use a file as a block device for a guest
domain.  Hoewver, the new virtual disk management in 1.2 allows
file-based disk images to be imported to Xen virtual disks and
vice-versa.  Virtual disks are allocated within a pool of free space
made up of devices and partitions on your system that you have set aside
for the purpose.  You can extend this free pool when you want.  Virtual
disks can also be enlarged by allocating more space from the free pool
(Currently, they can't be enlarged whilst mounted by a domain and have
that domain see the changes.  But that wouldn't be hard to implement).

> Maybe these could be served from Domain0 in some efficient fashion I
> don't know...  I guess you could do it using the nbd but a more
> efficient mechanism would be nice.  Something like iSCSI but over a
> Xen transport.

Right now, you probably could serve them from domain using something
like NBD, but that won't be necessary once the next gen IO stuff is in
place.  That will allow lots of cool things, including efficiently serve
out files as block devices AND have them appear as ordinary Xen virtual
block devices to guests, so your guests don't have to run any weird
network protocols and can easily use them as their root file system.
There was a thread related to this a few days ago that you might also
find interesting.



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