External disk stalls iMac I have a weird problem with an external disk connected to my 27" iMac running OS X 10.6.5.

It is a 1TB LaCie d2 Quadra and it is connected through Firewire.

I use this disk primarily for Time Machine backups, which works well and fast.

The problem is that when this disk wakes up, it locks up the complete iMac. While I hear the disk spin up my iMac is unresponsive. Then when the disk is ready, the iMac comes back to life.

What is going on here?
What is going on is that OS X (actually it’s the Finder and the I/O subsystem) is “waiting” for the drive to be readable. 

Truth is, is not the “whole mac” but the Finder (and any Finder application) what freezes. For example, a Save/Open dialog, Time Machine starting, a Finder window, etc. However you can always cmd-tab and perform other actions.

There isn’t much you can do, except to tell OS X not to sleep your hard drives (or wait for the drive to spin up):

. Beware with that option, because it will mean that your hard drives are on all the time, thus degrading their lifespan. 

I’m not 100% sure if that option affects Firewire/USB external drives, but I think it does.