HDD Write Speed

80 to 100 MB/s. A Gigabit Ethernet (Cat 5e, Cat 6) cable will suffice for fast transfer between those two.

You can use the following applications to benchmark the speed of your HDDs:

• AJA System Test
• Blackmagic Disk Speed Test
• Xbench

 

HDDs get no more than about 70MB/s read and about 50MB/s write from what I've seen (especially the ones Apple puts in their laptops). At those speeds, you can't even max out USB 2.0, let alone Thunderbolt.

 

2.5" S-ATA HDDs spinning at 5.400 RPM can easily reach 70 to 80 MB/s read AND write speeds. 2.5" S-ATA HDDs spinning at 7.200 TPM can reach up to 100 MB/s.
USB 2.0 will peak at 37 to 38 MB/s, Firewire 800 will get you 60 to 70 MB/s.

PS: I have several 2.5" S-ATA HDDs, one even is a 7.200 RPM one (Momentus 7200.4), and I have tested them via e-SATA to get those numbers.

 

I suppose the USB comparison was a bit of an exaggeration, but the point still stands that Thunderbolt is overkill.

 

That I agree with, thus my recommendation for Gigabit Ethernet.