Disk Benchmarking Question

I'm pretty new to benchmarking hard disks and I'm looking for some advice
on interpreting the results of some basic tests.

The server is:
- Dell PowerEdge R430
- 1 x Intel Xeon E5-2620 2.4GHz
- 32 GB RAM
- 4 x 600GB 10k SAS Seagate ST600MM0088 in RAID 10
- PERC H730P Raid Controller with 2GB cache in write back mode.

The OS is Ubuntu 14.04, I'm using LVM and I have an ext4 volume for /, and
an xfs volume for PGDATA.

I ran some dd and bonnie++ tests and I'm a bit confused by the numbers. I
ran 'bonnie++ -n0 -f' on the root volume.

Here's a link to the bonnie test results
https://www.dropbox.com/s/pwe2g5ht9fpjl2j/bonnie.today.html?dl=0

The vendor stats say sustained throughput of 215 to 108 MBps, so I guess
I'd expect around 400-800 MBps read and 200-400 MBps write. In any case,
I'm pretty confused as to why the read and write sequential speeds are
almost identical. Does this look wrong?

Thanks,

Dave