A post I posted here in the VMware forums and I’m waiting for some reasonable explination on why everyone is afraid of Extents in VMware.
Extents and the Mystery

My major observations on why people are afraid of extents is because of bad administration. People are afraid because of mistakes like putting a LUN with one RAID/disk config with a LUN of a different RAID/disk config. People are also afraid of LUNs magically disapearing, which doesn’t usually happen in the SAN world when you’ve got good administrators.

Here is a diagram of the idea behind a VMDK with extents.