Depends on your needs. I suggest you tell a bit more about what you need in details and maybe someone have recommendations. (what OS and applications do you wanna backup? what backup hardware do you have, how many GB/TB per day? ...)
thank you for your reply.
I have a two node cluster with drbd and 6 vms running on it (4 win2k8,2 linux).
Total space of all vms approx. 2 TB.I want a solution to incr/differential backup at vm level. on a NFS storage.