[Beowulf] clustering using xen virtualized machines

[Gerry Creager]

Mark Hahn wrote:
>> I don't buy the argument that the winning case is packaging up a VM with
>> all your software.  If you really are unable to build the required
>> software stack for a given cluster and its OS, I think using something
> 
> you're right, but only for narrow-function clusters.  suppose you have a 
> cluster used by 2k users across a handful of different universities
> and 100 departments.  and have, let's say, 2 staff.  it's conceivable
> that using VMs would permit a higher level of service by putting more 
> configuration flexibility into the hands of the users.  yes, most would
> use a standard image (which might be the bare-metal one, actually),
> but making it easier to accommodate variance is valuable.
> 
> it even offers the ability to shift the model - instead of actually 
> booting VMs on nodes for a job, how about just resurrecting a number
> of VM instances (freeze-dried in already-booted state)?  that makes the 
> setup latency potentially much lower.  (pages from a VM image can
> be fetched lazily afaik, and presumably also COW.)
> 
> for the few HPC-oriented performance studies of VMs I've seen,
> the only slowdowns were for OS activity (IO, page allocation, etc).
> an ideally-behaved HPC app minimizes those already, so...

Coming in a bit late, but I have one minor quibble, Mark: VM network 
latency. I've seen this be a bottleneck for some of our (non-HPC) VMs on 
decent hardware and network gear, at least with Xen, and VMWare, before it.

The attractive part of the VM Picture is what you stated, though, where 
the user takes the onus of managing their own image with software.  I'm 
considering this for an urgent-computing model I want to field...

gerry