i have also discovered this info (though it is a little dated now)
So I've been plugging and unplugging these devices constantly. I this period, the FW bus on my G4 has died twice. Since the ports are on the logic board, this is a $1200 repair (under warranty, thankfully). After the last one, I asked the tech about hot plugging. Suffice to say, what he told me has meant I now have a $50 4 port FW card in my machine and I just use that. Certainly any iMac I care about does not get hot-plugged into any FW device with it's own AC power. Maybe it's the higher voltage here: maybe I'm being over cautious - but if the FW dies on ane of those, you're screwed.
[We quoted reader Tim Chong last June, who said, "According to this article by Medical Mac, and this announcement by Ratoc Corporation (both articles are pretty long and technical and in Japanese), basically it says that if you plug bus-powered FireWire devices into a Mac while the Mac's power is on there is a possibility of the FireWire port being damaged." -MacInTouch]
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this was from
http://www.macintouch.com/firewirereader02.html
from a post on Fri, 07 Mar 2003
i wonder if this is the answer?
Further on in this post it says:
Date: Fri, 7 Mar 2003 09:59:07 -0600
From: Dennis J. Boccippio
Subject: FireWire port shorts
Regarding the recent flurry of posts on FireWire ports being "blown" from hot-swaps:
I (unfortunately) have had direct experience on this topic on several occasions. Shortly after installing OS X (about a year ago, and reported to MacInTouch, I think), I attempted to create a terabyte-plus daisy-chained array of FireWire high capacity drives (ranging from 75-120 GB, at the time) as a low-cost alternative to a pricey SCSI array ... about 10 in all. (I'm a scientist on a limited grant budget, and need lots of concurrent but non-critical online storage without investing in an expensive server solution).
I quickly learned that hot-swapping was a huge mistake in this configuration. Not only did I fry my G4/DP800's onboard FireWire bus, as well as a replacement OrangeLink card, I took out several of the drives' FireWire bridges in the process (interestingly, leaving the IDE drives within the FireWire enclosures mostly intact, and recoverable if used as internal IDEs). The problem here is that once something in the chain goes, it's nearly impossible to determine whether the problem is in an individual drive's bridge, or the onboard bus itself, or to reassemble the drive chain, without putting other drives at risk.
I finally learned that avoidance was the best solution. The following steps have prevented further failures. I have no idea which are true "solutions" and which are simply overkill, but they're probably all good ideas.
External FireWire drives should simply not be hot-swapped, whatever the specs may say.
Long daisy chains are not a good idea. I invested in a FW hub from Granite Digital and now have 3 sets of 4-disk chains. The hub at least gives me some solace that there's something in between the various chains which might intercept a short (? no idea if this is electrically valid, but it makes me feel better). OS X seems mostly happy with this configuration, though on rare occasions I run into problems with intensive copies from one FW drive to another.
The 3' (or longer) cheap FW cables which ship with most external FW drives are overkill and a bad idea for daisy chaining. (Probably obvious in retrospect). I invested in high-quality 6" patch cables from Granite Digital to keep the cable runs as short as possible.
I keep all drives on a given chain plugged to the same power strip. I try to keep as much of the overall system as possible connected to the same UPS and/or wall outlet(s). I don't know enough about electrical wiring to know if this is at all meaningful, but if small voltage differences are a potential culprit, this seems like a good idea.
Even given all these steps, I'm still edgy about hot-plugging expensive devices such as my DV Cam into the system, and depending on my ambient paranoia level, will cold-swap them instead.
I still think FireWire drives are a much better solution for maintaining large amounts of concurrent online storage, than, say, a SCSI array, especially given the miserable history of 3rd party SCSI card manufacturers' updating their drivers for new MacOS releases, and the cost of equally-sized SCSI drives. But users should not assume that the "wonder-specs" of FireWire mean that constructing such a system is either trivial or should be treated casually.
[After a couple weeks of hot-swapping a new AC-powered external Firewire hard drive and connecting our iBook in Firewire target mode, we somehow killed the Firewire ports on our G4 450 DP desktop Mac. An inexpensive PCI Firewire card solved the problem -MacInTouch]
