Hello, my problem is that I have about 20 virtual disks, and I use rsync to backup them,
but if I only change a byte of one disk, rsync will transfer the whole disk.
Is there any software to just transfer what I changed instead of the whole file?

Yes rsync does this.
This is the command I use to backup my "home-source" data directory to "home-destination" directory on a second drive partition.

"home-source" backup to sdb6 "rsync -auvpH home-source/ /mnt/hd/home-destination/"
This does incremental backups, with the same permissions.
Do some reading on the web to find what the options are doing; and if it suits you.

hywei, did you get this worked out? Not clear from your original post whether it would be a problem with how you are specifying the details to rsync, or whether perhaps you are dealing with disk images for virtual systems. If the latter, and you are using rsync from outside those virtual systems, then rsync will see the disk image as a single file, and that could be a problem. If you run rsync from within the virtual system, then you can be more appropriate and conservative in what you copy. It is sort of like the idea of backing up your data rather than your whole system on the assumption that you will reinstall the OS and recover the data.

However, there may be some tricks you can apply to get virtual system disk images copied efficiently, if that's what you are doing and what you want to do. See, for example, http://www.finalcog.com/rsync-vm-spa...ace-kvm-vmware.

hi, choogendyk.

My problem is the latter case as you said, and I try to use rdiff-backup to solve it before, but currently I don't have enough time to complete it.

However, thanks very much for your suggestion, and I will post it if it works.