How to defragment Virtual Machine in order to optimise virtual HD backups?

I've got the following setup:

• a virtual machine with a virtual HDD at 160GB split over around 50 files (it's a VMWare VM, so I'm talking about VMDK files)
• after working in the VM for some hours, my daily backup will copy all 50 file, because they all have modifications

My question is this:

• Is there a tool to "defragment" the windows file system in a way to keep the busy files roughly together?
• (The idea is that fewer HDD files are modified in order to improve backup performance)

My questions are not:

• How to defragment a HDD in general...
• How to improve backup performance in general...
• I'm not looking for suggestions on backup software...

Take a snapshot of your VM. This will prevent further writes to your existing .vmdk files, and they therefore will need to be backed up only once. Your regular backups then would backup only your delta disks, which usually would be much smaller (at least initially). To minimize unnecessary, future large-scale changes to the delta disks, before you take the snapshot, you should:

• Defragment your guest file system.
• Wipe and shrink your virtual disks.

Also note that the base disks can still be modified on the host if their .vmdk files are defragmented later, so before performing your initial backup, you should defragment the .vmdk files themselves through the VMware Workstation UI.

Your delta disks will naturally grow as you use the VM, install guest OS updates, etc. At some point you can choose to take another snapshot (and separately choose whether to merge it with the previous snapshot).