When it comes to efficiently synchronizing data between hard-drives there is a great Unix/Linux command-line tool, rsync, which is installed on OS X Tiger (and perhaps previous versions too) by default. OS X only contains the command-line tool though, not a GUI to provide easy access to it. This is where arRsync comes in. All it does is provide a simple GUI and the ability to store profiles, but that’s all that’s needed to make rsync available to regular users. You might wonder why you would need to efficiently synchronize data between two hard-disks? The answer, backups! I use rsync (via arRsync) to backup all my important data to external hard-drives. The nice thing about rsync is that it only replaces files that have changed, so even if you have hundreds of GigaBytes of data, you’ll still be able to update your backup in a reasonable time. Oh, and arRsync is both free and open-source!

[tags]Backup, arRsync, Rsync, OS X[/tags]

To create a backup just select what folders you want backed up to where and save it as a profile. Then you just have to load the profile and click a button to update the backup copy of your data. Below is a screen shot of arRsync about to start my main backup.

arRsync Main Window (Small)
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arRsync Dock IconAs childish as it sounds, one of the things I really like about arRsync is it’s icon, it’s a skull and cross-bones with the regular circular sync icon instead of a head. The other nice thing about the icon in the Dock is that while you’re doing your backup it shows you a progress bar! Since large backups (few hundred GB) can take a significant amount of time, particularly if you’ve updated a lot of files or if it’s the first time you’re backing up the data, this is actually a very useful feature.

All in all arRsync is a very good program because it does what it does very well, and despite being beta software it is still exceptionally stable. I’ve been using the current release since it came out a few months back and it hasn’t crashed on me once despite the fact that I regularly backup about 300GB with it. However, there are a few drawbacks. The first is purely the fault of the tool, despite the fact that the rsync command supports synchronization across networks (via SSH), arRsync does not. I guess the developers chose to concentrate on getting the important stuff right first which is fine with me. The second problem is not actually arRsync’s fault but rather Apple’s! There is a problem with the way the Mac version of rsync deals with resource forks on some files. This results in errors being generated by rsync, but the good news is you can ignore them, your backup has still worked! This problem tends to come up most with files that you copy to your Mac from a FAT32 device like a pen-drive or a Windows machine. The screen-shot below shows the typical error you get when this happens:

arRsync Error Message
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If you want to be absolutely certain your backup was successful even if you get the error message you can view the error log and if the names of all the files it had problems with start with ._ (as shown below) then you can rest assured that all is well with your backup.

arRsync Error Log
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I find arRsync to be an excellent program that works so well for me I have no other backup software installed. What makes me even more excited about this software is that it’s this good while still in Beta, just imagine how good it can get in the future!