Here are a few defrag tips when working with VMware ESX/ESXi.
- Use your guest OS defragmentation tools to defrag VMs.
- Always defrag your VM before you create a template.
- Do not defragment a drive while a VM has snapshotting enabled (your VM will grow in size, and slow stuff down
- Defragment before you take a snapshot
- VMFS filesystems do not need to be defragged, because their block-size is large and VMDK's are pre-allocated.