External Hard Drive Speeds

Thunderbolt 3

40 Gbps

Same connector as USB-C; Can be combo port

Thunderbolt 2

20 Gbps

Mostly on Macs

USB 3.1/USB-C

10 Gbps

Thunderbolt

10 Gbps

Mostly on Macs

USB3

5 Gbps

Most new computers, including Macs

eSATA

3 Gbps

Lost popularity to USB3

FireWire 800

0.8 Gbps
(800 Mbps)

Mostly on Macs, replaced by faster connections

USB2

0.48 Gbps
(480 Mbps)

Mostly used for slower devices such as mice and keyboards

FireWire 400

0.4 Gbps
(400 Mbps)

Mostly on older Macs and older video cameras

Speeds listed are top specifications, not real-world speed. For example, Thunderbolt is twice as fast as USB3 in spec, but in practically, it is 3-6 times faster (but that's nothing to sneeze at).

Most hard drives can't even keep up with the USB3 speeds, so paying a premium for Thunderbolt seems unnecessary until prices drop. (See Hard Drive Speeds below).

Gbps (gigabits per second) equals 1000 Mbps (megabits per second).
MBps (megabytes per second) is not the same as Mbps—MBps is eight times more than Mbps).

Hard drive speeds

A standard 7200 rpm hard drive's transfer (to buffer) rate is about 1024 Mbits.

A 7200 drive speed is:

• 20% faster than FireWire 800
• 3 times slower than eSata
• 5 times slower than USB3
• 10 times slower than Thunderbolt.

Of course, performance would increase if using a RAID system (ee Common RAID Types below) or using faster 10,000 rpm drives. As you might suspect, 10K drives transfer data at approximately 25-33% faster than 7200 drives, however they are harder to find through consumer channels.

Common RAID Types

• RAID 0 (zero)
  • Striped, no mirroring or parity
  • 2 drive minimum
• RAID 1
  • Mirrored, no striping or parity
  • 2 drive minimum
• RAID 5
  • Striped and distributed parity
  • 3 drive minimum
• RAID 10 (OR 1 plus 0)
  • Striped and mirrored
  • 4 drive minimum
  • Perhaps the most common RAID
  • Make sure mirroring is done before striping and not vice versa

  Definitions:

• Striped: data is written across multiple drives at once, splitting the file data.
• Mirrored: data is written to multiple drives at once, copying the file data. If/when a drive fails, the mirrored version should kick in (and warn the adminstrator that a drive failure has occured).
• Parity: data is when combined data bits are calculated in order to recreate original data in case of drive failure. Some RAID systems require a separate drive for the parity data, while others use existing drives (distributed). Parity is always combined with striping.