I noticed that, too, but then noticed that the OP seemed to be running
three copies of Bonnie++ in parallel. His command line was:

'bonnie++ -s 4G -m 3ware-swraid5-type -p 3 ; \
bonnie++ -s 4G -m 3ware-swraid5-type-c1 -y & \
bonnie++ -s 4G -m 3ware-swraid5-type-c2 -y & \
bonnie++ -s 4G -m 3ware-swraid5-type-c3 -y &'

I'm no expert, but if he's running three in parallel on the same
software RAID, I'd suspect that the total performance should be taken as
the *sum* of those three---or over 60 MB/sec.

Good point- I missed that!

steve