On 28 Jan 2010, at 3:10 pm, 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.)
COW is certainly how some of the virtual desktop solutions work;
desktop machines are 90% identical in most organisations, so it makes
sense to use COW when firing up a new one. So the technology is
definitely around.
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...
We've certainly seen some interesting behaviour as far as the network
is concerned. We tried creating a VM with a Lustre client in it, and
have not had much success with that. There's more variability in
network latency, and the Lustre servers hate that and keep ejecting
the client. We haven't solved the problem yet.
Tim
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