Do I need to keep enough free space on each datastore (VMFS) to backup the biggest VM on each of them. So if my biggest VM is 2TB, I will always need to keep 2TB free on the datastore so TSM for VE could do his backup job ? The vStorage API doesn't need a staging area do do his job (unlike VCB), but the snapshots seem to require a lot of space on the VMFS datastore.

For example :
The TSM for VE backup server (aka "data mover") makes a snapshots of the VM it wants to backup and then connects the VM disks to himself so it can backup them. So far so good... but ... if the VM that is being backed up is taking 2TB of storage space on the vmware datastore, the backup process will then require an additionnal 2TB on the datastore (2TB for the disks connected to the "data mover", and 2TB for the snapshots disks on the VM).

I'm surely doing something wrong ... some thoughts ?