Seems there should be an ability to do incremental backups. I realize for Windows VMs this may be a challenge but for Linux it may not be too bad. I sent Joe a script written by a buddy Chris Wik which does this. I have 17 VMs which are spread across 4 hosts which all tie into FreeNAS via their own dedicated jumper directly to the NAS. It takes nearly 9 hours to complete the backups every night.