Re: [Xen-devel] Xen & Automated Disk Management for Domains

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> One feature that would be really nice to have is the ability to easily
> manage the disk images used by the Xen domains, so that I could, for
> example, quickly load a particular Linux distribution on a set of LVM
> logical volumes, then start a new Xen instance with those.

I'd certainly like to see more support for this.

Copy-on-write (CoW) sparse disks are pretty high on everyone's
wish list. In principle, it should be possible to do this today,
but it's a pain to setup: use LVM snapshot with the log device as
a loop interface connected to a sparse file.

I've never actually tried this, but it should work. Has anyone?

[The LVM snapshot device is a bit 'odd' for our purposes as
writes occur in-place, with the old block contents being copied
to a log device. It would make more sense if we slightly modified
the code to have the writes go to the log and leave the original
device pristine. ]

It would certainly be very nice to have xend assist with setting
all this up, and have a nice way of naming images etc (leveraging
LVM wherever possible).
 
> This isn't terribly difficult to do with a few scripts running in Domain
> 0, and I already have a basic working version.  But as I'm looking at
> cleaning this code up, I'm wondering if it this functionality wouldn't
> be useful to others, and if it's worth integrating into the Xen control
> tools.
> 
> Are there any current tools to do this sort of thing?  Any plans for
> such tools (in xend, the future Xen Cluster Daemon, or elsewhere)?
> Would it be worthwhile to try to make my code more general so that it
> could possibly be included in Xen?  Integration with xend/xm has some
> benefits:
>   - management over the network comes almost for free
>   - could integrate better with domain management; for example, it would
>     be easy to check that logical volumes for a running domain aren't
>     accidentally deleted
> On the other hand:
>   - perhaps there are already plans to accomplish this in some other way
>   - the persistence requirements for disk images are different than for
>     domains, and so there's not a perfect match
> 
> Would anyone else find it useful if I worked on this?  If so, what features
> would you like to see?  Or am I going about this the wrong way?

xend is intended to be extensible for exactly this sort of
thing. Mike's writing a manual for it, which should be going into
the tree RSN.

Best,
Ian


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