VMWare - Never expand a disk with a snapshot running

You should never expand a virtual disk while snapshots are active.

In ESX3.5, although it will allow you to expand a virtual disk with snapshot and VC will report that the tasks completed successfully, but in truth the disk not actually expand.

It's worst if you expand disk with vmkfstools while snapshot active, the VM will no longer start and you will receive an error: "Cannot open the disk ".vmdk" or one of the snapshot disks it depends on. Reason: The parent virtual disk has been modified since the child was created." Fortunately there is a way to recover from this scenario, it is detailed in the VMworld 2007 presentation IO44: Top support issues and how to solve them – Batch 2.