How To Ruin Your Filesystem

It’s been a while since I last posted, and, as my iMac is currently ‘busy’ I thought now would be as good a time as any for my first post of the new year. First of all I have to say, Happy New Year, a bit late I know but better late than never. Now I can get to the true purpose of this post.

This post is a cautionary tale about external hard drives and, what I see as an error in Mac OS, more specifically, Leopard. In my endeavor to keep as many Time Machine backups as possible I have recently retired my old Western Digital My Book Premium 320GB in favor of a Western Digital My Book Studio 1TB. The hard drive itself is great, really quiet, large size. It is due to the large size that I am now in the situation I am in.

Because of all my new found space I realized I could keep Time Machine backups of both my iMac and my PowerBook on the same drive. To keep backups of the PowerBook my idea was to mount the WD drive over AFP on my PowerBook and Time Machine from there, this would have been the sensible thing to do, however backing up over 11GB of the network would have been time consuming so I opted to create a network, temporarily, with firewire, so it would be much faster.

It would appear however that firewire daisy chaining works in mysterious ways, when I connected the iMac and PowerBook with a firewire cable the WD drive was ‘passed through’ to the PowerBook and appeared mounted on both desktops. I thought this was a clever feature of Leopard and used it to my advantage & started the Time Machine backup.

The backup subsequently hung, so I stopped it, decided I couldn’t be bothered and I could live without Time Machine for my laptop. I tried using the drive again on my iMac, first deleting the image created by the PowerBook & received an error. Then after trying to verify the drive and finding it couldn’t be repaired, realized I had found what could be considered to be a bug & a combination of my own stupidity.

I am currently running DiskWarrior and the external drive if full of overlapped files. This is because the ‘pass through’ was not a clever Leopard trick, it was a result of the firewire implementation (that could have been blocked in the OS I am sure), and caused simultaneous writes to my external hard drive to occur.

Fortunately it only appears to have written off my Time Machine backups (it was Time Machine that started up on the iMac whilst the PowerBook was doing the same) and not the other data on the drive, which I managed to salvage (in case DiskWarrior fails) by mounting the drive in read only mode.

Take my advice, think before you do something like this, I should have realized this would happen but I thought Apple were good enough to stop me doing something this stupid.

Check back soon for more useful posts.