View Full Version : Turning Firewire HD On and Off While Mac's Running

01-22-2007, 06:47 AM
I have several external firewire (400 and 800) harddisks that I usually only turn on when I need them. Before turning them off again, I unmount them of course.

Now a tech guy at work told me I should only connect and disconnect firewire drives while the computer is turned off. He said even though firewire is being marketed in this way, unlike usb, it is not designed to be used in such a way and doing so could lead to serious problems.

Is that true?

01-22-2007, 08:31 AM
I think that it is true that connecting and disconnecting the firewire cable while the machine is powered should be avoided, but I don't think there is any problem with powering on or off an external device (especially if that device isn't drawing it's power directly from the firewire bus). If you unmount the device properly, that should avoid any data corruption. So, I think your tech guy is being somewhat more conservative than really necessary, but one does need to take care when plugging a bus-powered device into a firewire port while power is being supplied.

Joe VanZandt

01-22-2007, 11:16 AM
I largely agree with Joe above. However, there seems to be a bit of confusion between two things: using a power switch to turn on or off a FireWire device, and plugging/unplugging a FireWire device that is switched on.

There is danger of blowing FireWire ports by hotplugging and hot-un-plugging of FireWire devices, especially if said devices are turned on when hot-plugged, or permanently on as is the case with FireWire devices that do not have a power switch. If you absolutely must connect or disconnect a FireWire device, it should be powered off first.

However, using a power switch to turn on or off a FireWire device that is plugged in to a switched-on computer has basically no chance of causing problems. This is a primary reason why every FireWire device should have an on/off switch, and FireWire devices that don't have on/off switches should be avoided like a swarm of bees.

So, I wouldn't worry at all about turning a FW device on or off (after properly dismounting it, of course) with a power switch, and leaving the FireWire cable plugged in.

I'd worry a little bit about plugging in or unplugging a switched-off FW device, but it's usually safe. Most of the time.

I'd advise never ever plugging or unplugging a FW device that is turned on, or permanently on. If you have a device like that, make sure power to both the device and the computer are off before doing anything with the FireWire cable.


01-22-2007, 11:33 AM
Thanks a lot!