I'm confused by hit-and-miss performance with NW6.5.8 on ESX 4.0.

I'm trying to virtualize most of my servers this summer, and have been running various editions of VMW for years. I've heard about incompatibilities with ESX, Netware and NSS volumes on iSCSI storage, but the first few VM's I built ran well.

Now it's about a 50-50 shot: some servers run well, while others using the same hardware and resource pools do not. (it's not just disk I/O - even the console is sluggish)

ESX itself doesn't seem to detect any issues. Util is low, tools are loaded etc.

This morning I moved a VM from the iSCSI SAN to local storage. If there was any performance gain, it's marginal.

These servers are on new Dell blades running the latest ESX 4. I have ESXi 4.0 on older equipment attached to a Fibre Channel SAN, and the performance of those VM's matches or exceeds the best of those on the new equipment.

Can anyone explain why one virtual server runs great, but the next one can barely load Monitor?