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 -> (new)Disk 1 at the same time as (old)Disk 2 -> (new) Disk 2 

Faster, slower or the same as:

Total Time for: (old)Disk 1 -> (new)Disk 1 
THEN (old) Disk 2 -> (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.

  • I might add... This is the same speed Thunderbolt would give you on a Mac Pro, as your throttle point would be the SATA bus, not the Thunderbolt cable. – bispymusic Mar 12 '13 at 20:44
  • great answer - thankyou. Could you add some more information about the bottle neck / SATA bus - very interesting and helps me understand how it works. I'm cloning 3 1TB drives -> 3 2TB + 1 512GB SSD (but they're not all full), hence the total 4TB of data. – glenstorey Mar 12 '13 at 20:55
  • 1
    Regarding bottleneck. When transferring files your slowest connection is your actual speed. In the case of Thunderbolt, its 10Gb/s is faster than the 3Gb/s native speed of the internal hard drive. Therefore, the internal hard drive actually limits the usable speed that Thunderbolt would provide in this scenario. – bispymusic Mar 12 '13 at 21:03
  • Regarding SATA option, the Mac Pro has four internal hard drive bays. It sounds like you are only using three of them. Therefore, you could load in succession each of your old drives into the empty 4th bay and use Disk Utility to clone the old drives over to the replacement drive on the new Mac Pro. This will leverage the internal SATA bus speed of 3Gb/s (vs. FW800's 0.8Gb/s). This guide walks you through installing a drive DIY: manuals.info.apple.com/en_US/MacPro_HardDrive_DIY.pdf – bispymusic Mar 12 '13 at 21:05
  • Sorry, you are using four drive bays. Here's what I would do. On new Mac Pro, remove drives 3 & 4. Insert drives 1 & 2 from old Mac Pro. Boot up and clone these two drives over using Disk Utility. Shut down Mac Pro. Install new drive #3 and old drive #3 (into bays 3 & 4). Boot up Mac Pro. Use Disk Utility to clone. Shut down Mac Pro. Install new drive #4 and old drive #4 into bays 3 & 4. Use Disk Utility to clone. Shut down Mac Pro and finally put all four of the new drives back in, in the order you want them. Make sense? – bispymusic Mar 12 '13 at 21:08

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