Scott Silva wrote: > USB I believe is not a DMA based port, so the processor has to do a lot of > work, especially at higher speeds. Rsync can also be a resource hog, as it > keeps most of the hash tables in memory it uses to compare files with. True enough, though I wouldn't say USB is the whole problem here, or maybe even the main one. Disk-to-disk backup amounts to a whole lot of I/O, and those pipes need continuous help from the CPU to stay full. I have a similar system to the OP, except that it uses a hot-swap SATA disk instead of USB and rdiff-backup instead of rsync. Both improve the speed over the OP's solution, but even so, top shows the backup process regularly grabbing about 50% of one of the cores on a lightning fast Core i7 box to keep that pipe to the disk filled. When the backup is running, you easily feel the speed hit when doing other things at the same time.