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I have been using rsync to copy files for some time. My understanding is that rsync is faster than cp when some of the files to transfer are already in the destination directory, transferring only the incremental difference (i.e. the "deltas").

If this is correct, would there be any advantage to using rsync to moving the contents of a folder A, to say, a folder B, with B being empty?

The folder A has close to 1TB of data (and millions of files in it). The transfer would be done over a local network (A and B being on different filesystems, both mounted on a supercomputer, e.g. A is NFS and B is lustre).

Aside from that, what flags should I use to ask rsync to move (not copy) files from A to B (i.e. to delete A when the transfer has successfully finished)?

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I don't think rsync can replace mv. I would expect mv to be faster on most file system types when the source and destination are within the same file system, because rsync would have to make a copy no matter what, and mv could probably get away with changing a few directory entries. The closest thing I can find to an rsync mv is the --remove-source-files command, but that does not remove directories. –  jw013 Jul 25 '12 at 17:19
    
Thanks @jw013! Just to clarify, the files are on different filesystems, and the transfer would be done on a network. Do you know if that would still make mv faster? –  user815423426 Jul 25 '12 at 17:22
    
Well, mv can't operate across a network - it would have to rely a local mount (e.g. NFS). If the bottleneck is the network, rsync would probably be faster than mv because rsync can do compression. –  jw013 Jul 25 '12 at 17:25
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By the way cp has -u option to copy source file if it is newer than the destination file or when the destination file is missing –  rush Jul 25 '12 at 17:38

2 Answers 2

up vote 11 down vote accepted

You can pass --remove-source-files to rsync to move files instead of copying them.

But in your case, there's no point in using rsync, since the destination is empty. A plain mv will do the job as fast as possible.

In your case, what could make a difference to performance is the choice of network protocol, if you have a choice among NFS, Samba, sshfs, sftp, rsync over ssh, tar piped into ssh, etc. The relative speed of these methods depends on the file sizes, the network and disk bandwidth, and other factors, so there's no way to give general advice, you'll need to run your own benchmarks.

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In general as Gilles said there is no advantage to using rsync to move files when mv will get the same job done simpler and there is no potential speed gain between ordinary file systems.

There are however some times when there is an advantage. In particular, if you have any doubts about the stability of either the source, the destination, or the machine doing the work, using rsync gives you resume ability. This can be a notable advantage if you transfer is very large and, say, your power grid is unreliable. Using rsync will be a more stable way to avoid data corruption in the event of a failure and pick up where you left off.

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