This is a very cool hint. It is also unlikely to break future versions of TimeMachine as they work through the disk image toolkit which actively supports this option. (e.g., this should be transparent to the way TimeMachine uses disk images. Of course if that were completely true they'd work fine on other servers as well, so be careful.)

Another reason this may be of significant benefit is that various servers may not deal well with having thousands or tens-of-thousands of files in a single directory. I have a two-tier backup system where I run TimeMachine to a disk on a 10.5 mac, then have a cron (okay, launchd) job that rsyncs that sparse disk bundle to a mirrored NAS. (Google "sync_timemachine.sh".) The NAS runs samba over linux, and gets really really slow when there are so many files in a single directory. Switching this over to larger files would really help. (Of course the real solution would be for Apple to fix this and use a hierarchical structure so you'd never have more than 256 items in a given directory.)

One reason why Apple may use 8MB chunks by default is that if you have an encrypted home directory and you do it with a sparse disk bundle, then any change you make will only require time machine to backup the 8MB chunk that changed, and not more.

[ Reply to This | # ]