Apple's Time Machine

Apple's Time Machine is an interesting piece of technology. The GUI front end is friendly, simplistic, and brittle. I used it to back up my Macbook, but once the disk died, I couldn't use the GUI to access the network back-ups of the lost machine!

I think this is partly as I had to tweak it originally a bit to get it to back-up to something that wasn't a particularly Apple-supported network share, or perhaps it was because the Mac I was trying to access it was used a different version of MacOS.

Anyway, I was now somewhat frustrated - perhaps vexed even, as I couldn't access my back-ups. However, behind the scenes, all it is is a 'sparsebundle' disk image, containing a list of dated directories containing the entire filesystem as of that time. Very straightforward to access once you're in!

It wasn't quite that straightforward in practice - there were random error messages until it got itself into a sensible state, but still... not bad!

The technology that makes this work is rather nice. The collection of directories share as much data as possible with minimal overhead by having hard links on directories! And to decide what needs to be backed up, the filesystem tracks directories modified since the last back-up. The transparency and simplicity of the back-up system, within the constraints of it being efficient, are rather neat. It does feel (to me, at least) that while it pushes the technology forward, it stays true to the Unix approach.

And then they put a glitzy but brittle GUI on top. :)

Posted 2012-05-10.