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Re: [Xen-devel] questions about production use

To: "Williamson, Mark A" <mark.a.williamson@xxxxxxxxx>
Subject: Re: [Xen-devel] questions about production use
From: Nick Craig-Wood <ncw1@xxxxxxxxxxxxxxxx>
Date: Sat, 24 Jan 2004 08:46:04 +0000
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On Fri, Jan 23, 2004 at 08:26:15PM -0000, Williamson, Mark A wrote:
> > 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.

Sort of like LVM but run by Xen?  Tha sounds very interesting.

> 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).

That sounds like just the job.  We'd also want to be able to access
all the virtual disks from Domain0 for administrative purposes (backup
/ transfer to a new host etc) but I guess that is possible.

> > 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.


How much of this and the above is implemented now?  Should I be
checking out Xen 1.2 and reading the docs?


Nick Craig-Wood

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