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Say I have two (or even more!) Firewire 800 bus powered external hard drives. Will all of them be fully powered (and not require an external power source) when I daisy chain them onto my computer? Or will only the first hard drive in the chain receive power? Thanks.

By the way, the first drive in this chain would be my LaCie Little Big Disk Quadra. I have not bought a second drive yet.

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up vote 3 down vote accepted

It depends on how much power your Firewire port provides and how much power your drives draw. You should be able to find the numbers you need by looking up the specs on your devices and doing the math on what is provided vs what is needed. All the drives in the chain should get power, they may just not get enough if their requirements exceed what is available.

I can only find a general number of 4 watts for your drives. Looks like some iMacs only have 7 watt Firewire ports, so that could be a problem if you've got a similar iMac.

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Also, if the hard drives are traditional mechanical spindle types, keep in mind they draw a lot more power while spinning up, so even if the bus can support more than one at their average power usage, if you plug them all in at the same time, they may well overload the bus. – camster342 May 26 '11 at 22:20

This guy has ran 5 self-powered WD Passport Studio Firewire 800 drives off the 8W firewire port on the Mac Book Pro:

Then this guy has ran 4 self-powered firewire drives and gives power details: He reckons spin up takes 4 watts so that means that 2 should work with no issues on a Mac firewire 800 port. Then more will work but might not be able to spin up at the same time as the others.

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