One of the highly touted advantages of FireWire is hot pluggability.
Unlike cranky old SCSI, you are supposed to be able to plug in or
unplug FireWire devices to your heart's content with your Mac powered
up - or not?
While I have occasionally taken chances (or been obliged to when
something locked up) and hot-plugged/unplugged SCSI cables over the
past decade, I've never experienced any notable problems from doing so.
Consequently, I find it highly ironic that I think I have just
experienced my first-ever hot-plugging induced hardware failure - and
it's with a FireWire drive.
While my daughter was home from university (for what used to be
called "March break") last week, she asked me to burn a CD for her. My
usual computer of choice for CD-burning is the good old Umax S900, so I started it up, and, while
it was still booting, I (being in a hurry as usual) plugged in the
FireWire cable for the Que Fire! CD burner into the Macally PCI
FireWire adapter in the S900 - and OS 9.1 immediately crashed to the
MacsBug debugger, which reported a bus error. Rats!
I tried rebooting, and the same thing happened again, although I
discovered that the Umax would resume booting if I typed "es" in the
MacsBug command line field and then hit Return. But while my Desktop
icons appeared, the rest of the Finder didn't - no menu bar and no
Desktop picture. Very peculiar. However, I could open my hard drive
window and get at the System Folder.
I tried rebooting from an OS 8.1 Disk Tools floppy, and the Finder
appeared normally. I ran Disk First Aid, which affirmed that all was
well on the hard drive. You can't do much when booted from an OS 8.1
floppy disk, so I opened Startup Disk and selected the hard drive
partition with OS 9.0 on it. When I rebooted, it again crashed to the
debugger when the extensions started to load. I then tried booting from
an OS 9.0 install CD, and that worked fine.
Okay, I also have OS 8.1 installed on the hard drive's third
partition, so I tried it, and the machine booted up normally. I ran
Disk Warrior on
all three partitions to make sure that there were no directory
corruption issues, although at this point I thought that was a very
long shot. While Disk Warrior did find a few minor problems that Disk
First Aid had missed, there was nothing that would explain the
anomalous behavior.
However, OS 8.1, which was working happily, does not support
FireWire, while OS 9.0 and OS 9.1 do, and that observation, combined
with the fact that the problem first manifested at the moment when I
was plugging in a FireWire drive, seemed to narrow the scope of
probability.
I opened the OS 9.1 Extensions folder, moved the FireWire extensions
to the disabled folder, and rebooted. The S900 started up nicely, with
the Finder and the menu bar showing up as they should.
Just to eliminate another remote possibility, I installed a fresh
set of FireWire extensions and rebooted again. It once more crashed to
the debugger as soon as the extensions started to load.
In summary, my best guess at this point is that plugging in the CD
burner (which was powered up at the time with its external power
supply) somehow damaged the FireWire port and/or PCI card circuitry,
something that I had thought was not supposed to be an issue with
FireWire.
If the PCI card really is fried, it's not a major financial
catastrophe - you can pick up 
Macally PCI FireWire adapters for about twenty dollars these
days, but it is a pain, although not nearly as much of one as being
experienced by a sizable cohort of titanium PowerBook owners who are
reporting FireWire port failures that seem to be related to plugging in
the iPod, of all things.
The provisional moral of this tale: Be cautious about FireWire
connections, and it's probably prudent to at least wait until the
machine is fully booted before connecting or disconnecting a FireWire
device.
TiBook owners might be well advised to be extra wary and put the
machine to sleep, although I don't know if that would really prevent
the problem from occurring
USB 2 anyone?
