Is there a speed difference between copying files at the same time or after one another We got a new Mac Pro server and I am faced with cloning 4TB of data from one, to the other via. Firewire 800 cable and Target Disk Mode. Oh for Thunderbolt. 

Is there an impact on the total speed of copying if you clone two hard disks simultaneously vs. cloning one hard disk, waiting for it to finish and then copying the next. 

i.e. is

Total Time for: (old)Disk 1 -&gt; (new)Disk 1 at the same time as (old)Disk 2 -&gt; (new) Disk 2 


Faster, slower or the same as:

Total Time for: (old)Disk 1 -&gt; (new)Disk 1 
THEN (old) Disk 2 -&gt; (new) Disk 2. 


Although this question would be appropriate for SuperUser, I'm asking specifically for our Mac environment. I think this is the type of thing that varies by operating system, and I'm not interested in the implications which are OS dependent (plus, I feel like this is my community, not SU).
There should be no difference. FireWire 800 operates on the physical layer, so it is all just bits of data as far as it is concerned. I recommend moving them both simultaneously, so you don't have to remember to come back and set the second one up to clone after the first is completed.

How many drives are you cloning? Personally, I recommend installing the drives from the old Mac Pro temporarily into the extra slots of the new Mac Pro and cloning them all within the new Mac Pro's box. That way you will benefit from internal SATA's 3Gb/s speeds, which are much faster than FW800.