Tests are done across four 7200RPM SATAII drives on a PCI-X card sitting on a PCI (32-bit, 133MB/sec theoretical max) bus, probably the slowest bus configuration possible, and then again after being moved to a motherboard with dual PCI-X slots. Server is running Ubuntu 9.10 AMD64 Server.

Benchmark is a simple ‘dd’ sequential read and write.

write: dd if=/dev/zero of=/dev/md2 bs=1M
read: dd if=/dev/md2 of=/dev/null bs=1M

mdadm –create /dev/md2 –verbose –level=10 –layout=n2 –raid-devices=4 /dev/sd[ftlm]1

	PCI	PCI-X
write:	13.2 MB/s	144 MB/s
read:	4.0 MB/s	89.3 MB/s

mdadm –create /dev/md2 –verbose –level=10 –layout=f2 –raid-devices=4 /dev/sd[ftlm]1

	PCI	PCI-X
write:	48.3 MB/s	131 MB/s
read:	92.7 MB/s	138 MB/s

mdadm –create /dev/md2 –verbose –level=10 –layout=o2 –raid-devices=4 /dev/sd[ftlm]1

	PCI	PCI-X
write:	47.4 MB/s	135 MB/s
read:	98.7 MB/s	142 MB/s

And more comparisons:

RAID1 (PCI)

write: 38.9 MB/s
read: 64.8 MB/s

Single Disk (PCI)

write: 59.4 MB/s
read: 71.9 MB/s