MacBook – How dangerous is it to hot-plug FireWire 400 devices

It depends primarily on how the devices are connected.

Say we have three devices connected:

A(400) <--> B(800) <--> C(800)

Firewire is processed in chips. 800 speed firewire chipsets will pass 400 speed along the 800 bus at 400 speeds as data is passed along the chain. So anything C sends will be seen by B and A as 400 speed, and it will exist as 400 speed on the 800 bus between A and B. It doesn't increase the 400's total bandwidth, but it does take twice as long to transmit along the 800 bus as it would if B had sent it natively.

When B sends to A it will be at 800 speeds.

The problem is that if A is particularly communicative then it will drag down the total bandwidth of the 800 bus between B and C. If A transmits at full speed, the 800 bus becomes a 400 bus. If A transmits 25% of the time, then its 100mbps data consumes 200mbps of time on the 800 bus.

When C sends data to A, it will be at 400 speeds, and use up twice the bandwidth on the 800 bus than it would if it were transmitting native 800.

This is called multi-speed concatenation.

When B notices C sending 400 speed data, it simply passes that data along the 800 bus at 400 speeds. When that packet is done it can immediately send the next packet at 800. The transition is instantaneous, so there's no additional bandwidth lost, but again, if A talks a lot, it can reduce the total bandwidth on the 800 bus significantly.

B(800) <--> A(400) <--> C(800)

This configuration will reduce the total bandwidth through the entire bus to 400, regardless of the chipset used in each device.

Found the solution, and that is that both system will mount the drive simultaneously in a potentially data corrupting manner.

Source: Macintouch Reader Reports FireWire: Connecting Drive to Two Computers

Q: Vy Tri Truong I have a stack of 2 FireWire Hard Drives next to my Mac Mini. I also have a PC laptop that I sometimes use to access the drives. My Windows XP PC has MacDrive 6 installed which allows it to recognize Mac formatted discs (which these drives are). On one of occasion, I accidentally left the drives plugged into the Mac while connecting my PC to it. I found that both computers were able to access files and write to the discs. Is having 2 computers access the same hard drive simultaneously advisable?

Turns out it is not a good thing to do, may cause data corruption, according to the same source.

A:Daniel Figucio Is having 2 computers access the same hard drive simultaneously advisable? No, it is not advisable in this configuration at all. The file systems on the drives are not concurrent file systems. This means that the PC has no idea where the Mac may have written data and vice versa - which means that they may both try to write data to the same block on the disk because they think it is free, when the other has already written data there - which will obviously corrupt data. The Mac and the PC WILL NOT communicate and tell each other what they have done. So use at your own risk..

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