The 2.5Tb storage partition on my Xen box decided to pack up recently (or at least Xen decided it no longer wanted to read the partition) so after backing up the data decided to run some tests.

Drives: 4x Western Digital RE 1Tb

RAID 5:

This was the original configuration of the array, despite having fast drives in my desktop and 1Gbit network the read speeds were slower than expected (around 35Mb/sec).

The hdparm results were inconsistent:

Timing cached reads: 10118 MB in 2.00 seconds = 5064.59 MB/sec
Timing buffered disk reads: 224 MB in 3.02 seconds = 74.24 MB/sec

Timing cached reads: 10020 MB in 2.00 seconds = 5016.71 MB/sec
Timing buffered disk reads: 148 MB in 3.03 seconds = 48.83 MB/sec

Timing cached reads: 10126 MB in 2.00 seconds = 5068.86 MB/sec
Timing buffered disk reads: 200 MB in 3.03 seconds = 65.94 MB/sec

Timing cached reads: 10086 MB in 2.00 seconds = 5049.90 MB/sec
Timing buffered disk reads: 234 MB in 3.02 seconds = 77.55 MB/sec

Timing cached reads: 10042 MB in 2.00 seconds = 5027.45 MB/sec
Timing buffered disk reads: 210 MB in 3.01 seconds = 69.80 MB/sec

Average over the 5 tests: 67.27 Mb/sec

RAID 10:

As an alternative I switched the array to RAID 10, the downside of this configuration is that there is 1Tb less space than RAID 5.

Timing cached reads: 10170 MB in 2.00 seconds = 5091.34 MB/sec
Timing buffered disk reads: 320 MB in 3.01 seconds = 106.46 MB/sec

Timing cached reads: 10094 MB in 2.00 seconds = 5052.71 MB/sec
Timing buffered disk reads: 316 MB in 3.02 seconds = 104.59 MB/sec

Timing cached reads: 10072 MB in 2.00 seconds = 5041.96 MB/sec
Timing buffered disk reads: 314 MB in 3.01 seconds = 104.29 MB/sec

RAID 10 results are much more consistent.
Average over the 3 tests: 105.11 Mb/sec

RAID 6:

Another configuration offering 2 disk redundancy.

Timing cached reads: 10172 MB in 2.00 seconds = 5091.87 MB/sec
Timing buffered disk reads: 202 MB in 3.01 seconds = 67.06 MB/sec

Timing cached reads: 10052 MB in 2.00 seconds = 5031.76 MB/sec
Timing buffered disk reads: 202 MB in 3.01 seconds = 67.18 MB/sec

Timing cached reads: 10102 MB in 2.00 seconds = 5057.17 MB/sec
Timing buffered disk reads: 206 MB in 3.00 seconds = 68.59 MB/sec

RAID 6 results are also fairly consistent.
Average over the 3 tests: 67.61 Mb/sec

It seams that with this configuration that RAID 5/6 perform at roughly the same speed, however RAID 10 seams to win out on the speed test with over 50% improvement over RAID 5/6.