I'm Just Saying & Whatnot

jstn:

I installed Snow Leopard over the weekend and decided afterwards to reset my Time Machine backup, which I was surprised to find went back more than a year and had grown to 1.5TB. If you ever find yourself in this position, do everything you can to just reformat the whole disk. Because I share my Time Machine drive with other stuff I tried to just delete the “Backups.backupdb” folder normally, but emptying the trash wound up taking two full days. Untold millions of files! While I was waiting I figured out a cool command line trick, which I share with you here so we can both avoid repeating my fate. All on one line, substituting your own variables:

hdiutil create -size 500g -fs HFS+J -volname "Time Machine" /Volumes/Drobo/justinbookpro_001ec1325b6e.sparsebundle

What this does is create an expanding disk image with a maximum size that you can set, and that Time Machine will mount and use instead of the whole drive. You can also delete it in one quick shot if you ever need to. The trick is naming the file with your hostname, followed by an underscore and the MAC address of your ethernet adapter (get it with “ifconfig en0 | grep ether”). The volume name can be anything.

Now, when I set Time Machine to use my disk “Drobo”, it’s smart enough to mount that sparsebundle and put it away cleanly when it’s done, and it can’t ever get bigger than 500GB.

This is an absolute lifesaver for anyone backing up to an external disk they want to use for more than just Time Machine.