Can rSync clone a TM backup?

Discussion in 'macOS' started by gwelmarten, Jan 27, 2013.

  1. gwelmarten macrumors 6502

    Jan 17, 2011
    So, I've now heard Finder isn't the best for copying large complex files, and can allow corruption to take place. What I am wondering is, will rSync be capable of keeping two TM backups in sync? So, I backup daily to one HDD and then have that HDD rSync to the other one weekly? Or will I get a corrupted backup on the second one?
  2. costabunny macrumors 68020


    May 15, 2008
    Weymouth, UK
    sorry I don't know, but I am going to include myself in this thread as its a question I would like to know the answer too also. I want to be able to copy my TM to another drive once a week/fortnight.

    I guess rsync as root should do it, but would TM 'speak' to it in the future should things go pear shaped and a restore becomes necessary?
  3. switon, Jan 27, 2013
    Last edited: Jan 27, 2013

    switon macrumors 6502a

    Sep 10, 2012
    RE: rsync and TM...


    While I haven't tested this specifically, and I think this would be a great thing to test, I do believe it will work. I would be shocked, in fact, if it didn't work, but one never knows until one tests it. My reasons follow.

    The "rsync" utility and the rsync remote-update protocol has an "-a" (archive) mode that maintains all ownerships, permissions, and links (and even hard links) for files and directories. As such, it should then maintain the links and structure that go into a TM backup. (Of course, a TM backup to an connected volume is different than a TM backup to a networked volume, so this would have to be tested separately.) Secondly, the rsync utility checksums all files that are transferred, first on the sending side and then on the receiving side to make certain that there were no communication errors. So, I guess it boils down to if you believe two different files can have the same checksum? If not, then the rsync copied file would have to be equivalent to the original file.

    Now allow me a couple comments...

    (1) The TM utility itself already allows for multiple backup volumes. If you specify two volumes, then TM will alternate between these two volumes for its hourly backups. Thus you could use TM to make two backups instead of copying one TM backup to another.

    (2) The rsync utility has a "daemon" mode which means that you can run rsync as a daemon. You would then write a single cronjob line to rsync your TM backup and/or your boot drive daily, weekly, and monthly automatically and without your intervention.

    (3) You could use the "tmutil setdestination..." or "tmutil inheritbackup..." commands to switch between different TM backups.

    (4) I think the question to ask is how rsync handles differential backups of sparsebundles? For an attached TM backup (not a sparsebundle), the directory structure is maintained and I think rsync would "do the right thing" for this TM backup in terms of properly performing differential backups. But I don't know how rsync would handle differential backups of sparse bundles.

    Anyone willing to test copying a TM sparsebundle via rsync?


Share This Page