Tests are done across four 7200RPM SATAII drives on a PCI (32-bit, 133MB/sec theoretical max) SATA II card, probably the slowest bus configuration possible. Done on 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

write: 13.2 MB/s
read: 4.0 MB/s

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

write: 48.3 MB/s
read: 92.7 MB/s

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

write: 47.4 MB/s
read: 98.7 MB/s

And some comparisions:

RAID1

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

Single Disk

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

Have an LVM device left on your system from a drive that was removed before pvremove was run?

$ sudo dmsetup remove /dev/mapper/removed-device