OS X Firewire External "self-eject" issue and possible fix

A possible work-around to the OS X Firewire External Hard drive and "self-eject" issue.

I have a small business that is almost entirely Mac and OS X, the only exceptions are the one MS Windows PC box sitting in the corner of my basement storeroom that runs some vendor software that must be on Windows and 3 VMs for a present client.

I have been experiencing this "self-eject" issue ever since I started using MacBook Pro laptops (unibody models). I cannot exactly pin-point the precise parameters as I've used several laptops and external firewire drives over the last 3 years (2009 to present 2011). As would anybody else, I started researching online about this particular "self-eject" issue.

With a Firewire External HDD connected to a unibody MBPro running on bus-power, with the MBPro on power-supply or battery, the "self-eject" issue occurs. I have been able to replicate this behaviour countless times, with different Firewire External HDD, and different MBPro, and with Snow Leopard and Lion. 

I've used many different Firewire cables in the process as well, with no observable differences. The version of OS X may be a factor, but I cannot observe any significant differences or events either. I've had Finder becoming "non-responsive" during some extended read-write operations, but I cannot definitively attribute it to Firewire "self-ejects", as the Firewire units were still connected and responsive. 

What I have observed with my particular hardware set, and I don't think it is related entirely to the version of OS X, is that the power source for the Firewire External HDD unit is a significant factor in whether it "self-ejects" or not.  I have arrived at the opinion that the Firewire external drive hardware and power supply appears to be more relevant to the "self-eject" issue. I could be wrong, but at least I can share what "configurations" have been working for me so far.

Configuration One

• iMac (late-2009 model)
• OS X Snow Leopard
• Iomega 500Gb Firewire External HDD
• Firewire bus-powered, no independent power-supply
• Time Machine on external Firewire HDD
• No issues 7 months (approx) continuous

Configuration Two

• MacBook Pro 15 (mid-2010 model)
• OS X Snow Leopard
• G-Tech 2Tb Firewire External HDD
• Independent power-supply
• Time Machine on external Firewire HDD
• No issues 5 months (approx)
• No issues "non-consecutive", as laptop has been moving in and out of the office.

Configuration Three

• MacBook Pro 15 (mid-2010 model)
• OS X Lion
• G-Tech 2Tb Firewire External HDD
• Independent power-supply
• Time Machine on external Firewire HDD
• No issues 1 month (approx)
• No issues "non-consecutive", as laptop has been moving in and out of the office.

Configuration Four

• MacBook Pro 15 (mid-2010 model)
• OS X Lion
• G-Tech 2Tb Firewire External HDD
• G-Tech 750Gb Firewire External HDD (daisy chained on 2Tb unit)
• Independent power-supply on 2Tb unit (powering 750Gb unit as well)
• No issues, read-write operation between both units (7 22 hours consecutive) *edited*

Configuration Five

• MacBook Pro 15 (mid-2010 model)
• OS X Lion
• G-Tech 750Gb Firewire External HDD ()
• Independent power-supply on 750Gb unit
• No issues 3 days (approx)
• No issues "non-consecutive", as laptop has been moving in and out of the office.

"Self-eject" manifestations

Any time I use the Firewire External HDDs on a MacBook Pro on bus-power. I get the "self-eject" problem showing up, regardless of OS X version, Snow Leopard or Lion.  

I cannot attest to Tiger nor Leopard, since I was using them on a 2008 Aluminium MacBook Pro. All I can say is that, I did not experience any "self-eject" issues with the aluminium non-unibody MBPros with any of my previous Firewire External HDDs (Iomega and Seagate) with Tiger and Leopard. This Iomega unit is the exact same one that is connected to the iMac listed in "Configuration One". However, when this same Iomega unit is attached to either one the two unibody MBPros, on bus-power, the "self-eject" issue crops up. The Seagate Firewire unit crashed with an internal hardware failure, prior to my using the unibody MBPros, so I was not able to test them together. The Seagate unit hardware failure is totally un-related to "self-ejecting" consequences (it stopped working completely after it fell off a filing cabinet).

Take my observations for what you will, but I hope it helps someone else figure out their Firewire "self-eject" issues.

If you have comments, please leave constructive feedback or suggestions that are helpful to others. As a forewarning, "flaming", "trolling", etc... comments will be moderated.