When virtualisation was new, we tried to virtualized everything.

Then came the cases where the virtual machine was very much slower than a physical one.

It boils down to the following ruleset (with us) when not to virtualize:

• Network-io-intesive applications (i.e. with many interrupts/packets)
• Disk-io-intensive (if not on SAN storage)
• RAM-intensive (this is the most precious resource)

Now this is true for a combination of XEN using local DRBD storage. The same seems to be true for Hyper-V using DAS.

I wonder - is it true for all combinations - and what are your limits on these combinations?