Wednesday, April 16, 2008

Wireless Disk Speed Test

There are so many ways to access data with Apple hardware. It could be on an internal drive. It could be on an external drive, either FireWire or USB. It could be on a disk attached to an AirPort Extreme (AirDisk), or a TimeCapsule. It could even be on the disk inside a TimeCapsule. How do the speeds of these various methods compare?

I used XBench, a free benchmarking tool, to compare the speeds of these different forms of storage. I don't have anything in particular to say about this tool, nor can I vouch for its usefulness generally. But it was free. Regardless of its details, it provides a common measuring stick, especially because I have run it from the same machine (i.e. a stock early 2008 black Macbook) for each test.

Unfortunately, other issues have varied across groups of tests. For the first group of tests, the external drive was a 300GB/7200rpm IDE drive in a Metal Gear Box USB2.0/FireWire enclosure. For the second group of tests, the drive was a 750GB/7200rpm SATA drive in a USB2.0 enclosure. 

                   XBench Disk Test Score
A: Internal Disk            28.70
B: FireWire Disk            49.01
C: USB Disk                 33.82
D: AirDisk (802.11n/2.4MHz)  3.91
E: AirDisk (100bT)           6.94

The internal disk is a 2.5" SATA disk, which explains why it scored so much lower than the USB and FireWire disks. Note that the USB and FireWire disks are actually the same disk, in the same enclosure. Of course, the two tests use different chipsets in the enclosure, and the pair serves to demonstrate the speed advantage of FireWire. Moreover, FireWire outperformed USB in every disk subtest. This same enclosure was attached by USB to an original AirPort Extreme BaseStation, which supported 100bT Ethernet. The wireless connection was 1/10 the speed of the direct connections. While the wired Ethernet connection was twice as fast as the wireless, that was still about 1/5 of the direct USB connection.  

For the second group of test, I attached the same 750GB/7200rpm SAT/USB drive to the same Apple BaseStation (BS) and to an Apple TimeCapsule (TC) , which also had its own internal 500GB/7200rpm SATA drive. 

                         XBench Disk Test Score
F: USB 2.0                         30.67

G: BS AirDisk (802.11b/g/n)         3.55
H: BS AirDisk (802.11n/5MHz)        5.10
I: BS AirDisk (100bT)               7.03

J: TC AirDisk (802.11b/g/n)         2.41
K: TC AirDisk (802.11n-only 2.4MHz) 3.27
L: TC AirDisk (802.11n/5MHz)        6.64
M: TC AirDisk (1000bT)             12.96

N: TC Disk (802.11b/g/n)            3.03
O: TC Disk (802.11n-only 2.4MHz)    3.56
P: TC Disk (802.11n/5MHz)           6.32
Q: C Disk (1000bT)                 15.10

Clearly, switching to 5MHz band -- at the cost of backwards compatibility with 802.11b & 802.11g, and the ability to penetrate as many walls -- gives a huge speed boost, both for the Extreme BaseStation and the TimeCapsule. Simply turning off compatibility itself results in a speed boost, though not as great. A wired connection, however, is always much faster than a wireless connection, topping out at 5x as fast as the b/g/n network. Note, however, that the same disk was still more than 2x as fast when hooked up directly with a USB connection.

Wireless benchmarking is notoriously flakey, and so you have to put assume some margin of error in each of these scores. That would explain why each of the disks had the top score in at least one test, despite clear trends suggesting that the TimeCapsule disk is the fastest and BaseStation's AirDisk is the slowest. 

No comments: