Set up counters on your server (performance counters) to view the read/write speeds of your centos server's hard drives. You very well could be transferring more data than your server can write.
Options to speed up your server's write performance would be moving into a striping RAID which most likely will cost you additional money.
I would look at the hardware of your server next if you can validate it is not your network causing the issues.
For anyone whose interested, I solved the problem. When I installed centos my bios settings for sata hard drives was as IDE compatible. Switching them to IDE enhanced enabled DMA.
My drives we /dev/hdX were now /dev/sdX. The root drive mounted itself. I had the other drives mounting to /home and /disk2 so I edited /etc/fstab.
After that, I got close to 75MB/s consistently to both drives.