I want to start regularly backup my home directory on my ubuntu laptop, machine X. Suppose I have access to 2 different remote (linux) servers that I can backup to, machines A & B. Machine X will be the master, and should be synced to A and B. I could just regularly run rsync from X to A and then from X to B. That's all I need.

However I'm curious if there's a more bandwidth effecient, and hence faster way to do it. Assuming X is going to be on residential style broadband lines, and since I don't want to soak up the bandwidth, I would limit the transfer from X. A and B will be on all the time, however X, will not be, so I'd also like to reduce the amount of time that X is transfering, potentially allowing A and B to spend more time transfering. Also, X won't be connected all the time.

What's the best way to do this? rsync from X to A, then from A to B? Timing that right could be troublesome. I don't want to keep old files around, so if I was to rsync, then the --del option would be used. Could that mean something might get tranfered from A to B, then deleted from B, then transfered from A to B again? That's suboptimal.

I know there are fancy distributed filesystems like gluster, but I think that's overkill in this case, and might not fit with the disconnected nature.