I am looking for recommendations for backing up my current 6 vm's(and soon to grow to up to 20). Currently I am running a two node proxmox cluster(which is a debian base using kvm for virtualization with a custom web front end to administer). I have two nearly identical boxes with amd phenom II x4's and asus motherboards. Each has 4 500 GB sata2 hdd's, 1 for the os and other data for the proxmox install, and 3 using mdadm+drbd+lvm to share the 1.5 TB's of storage between the two machines. I mount lvm images to kvm for all of the virtual machines. I currently have the ability to do live transfer from one machine to the other, typically within seconds(it takes about 2 minutes on the largest vm running win2008 with m$ sql server). I am using proxmox's built-in vzdump utility to take snapshots of the vm's and store those on an external harddrive on the network. I then have jungledisk service (using rackspace) to sync the vzdump folder for remote offsite backup.

This is all fine and dandy, but it's not very scalable. For one, the backups themselves can take up to a few hours every night. With jungledisk's block level incremental transfers, the sync only transfers a small portion of the data offsite, but that still takes at least a half an hour.

The much better solution would of course be something that allows me to instantly take the difference of two time points (say what was written from 6am to 7am), zip it, then send that difference file to the backup server which would instantly transfer to the remote storage on rackspace. I have looked a little into zfs and it's ability to do send/receive. That coupled with a pipe of the data in bzip or something would seem perfect. However, it seems that implementing a nexenta server with zfs would essentially require at least one or two more dedicated storage servers to serve iSCSI block volumes (via zvol's???) to the proxmox servers. I would prefer to keep the setup as minimal as possible (i.e. NOT having separate storage servers) if at all possible.

I have also briefly read about zumastor. It looks like it could also do what I want, but it appears to have halted development in 2008.

So, zfs, zumastor or other?