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For our intended uses VMs must have input from the outside world and must be able to write output somewhere which is accessible to non-VMs , however the VM is perhaps running an unpatched legacy OS with known security holes. Update: Redhat has announced that rhel5 and rhel6 will have a 10-year production cycle (as opposed to rhel4 , which was only 7). rhel6 will be maintained as a production OS into November 2020, beyond the 10-year lifetime of Fermi.
There is no need for the VMs to be general purpose machines. Restrictions like the following should keep the machines and other SLAC resources from being trashed without interfering with the functions we require.
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Currently (according to BaBar experts who are much further along in their VM plans) multi-core VMs don't perform nearly as well relative to single-core machines as their hardware counterparts, so the better strategy is to instantiate many single-core machines. But each one needs a license. That many rhel6 licenses would be prohibitive, so the they went to Scientific Linux instead. We may want to do the same. Or things may have changed by the time it matters to us.
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