When you plug in an external hard drive that hasn’t been unmounted properly, Snow Leopard actually starts running fsck on it:
/System/Library/Filesystems/hfs.fs/Contents/Resources/../../../../../../sbin/fsck_hfs -y /dev/disk1s2
Of course, nowhere does it actually inform you it’s doing this, unless you hunt down the fsck process.
So what probably happens is you decide it’s not going to mount and yank the cable a couple of times to see if it’s something wrong, of course this just disconnects the drive in the process of the fsck, which is something I’d rather not do.
this also happens in 10.4, and I guess 10.5 too, not just a 10.6 thing
I just stumbled upon this, and it seems like a singularly bad idea, especially with the big disks available today. My 2TB disk just went into limbo when I plugged it in, and had I not happened to notice this process I could easily have mangled it by unplugging it. In my case, plugging is the external disk produced to dialog box nor any sign of what was going on. My curiosity got piqued when I tried to run an fsck manually, and a strange error.
Worse yet, as far as I can tell, this silent fsck process does not log to the normal console, but only to hfs_fsck.log (which you can find with Console.app, but not unless you know to look for it).