WD15EARS slow write speed

Hi I have just installed a WD15EARS on a new system running Windows Server 2008 R2; as far as I am aware perfectly compatible with advance format

The drive is partitioned in 2, and formatted with NTFS.

I get very fast read speeds like 125MB/s, but my write is 9.4MB/s not good.

What have I done wrong.

PS: In BIO the intel controller is running sata connection in IDE mode rather than ACHI i tried to change after installation but windows bit my hand off so I put it back. Could hat be the problem.

Thanks for any help to resolve this problem

ok i fixed this: here how if you have this issue your self, I tried to activate ACHI post install using commonly found guide, and was able to increase write speeds to ~40MB/s fins for a desktop not cool for a server. 

So I reformatted and reconfigured with ACHI on form the offset and now it nearly hits 100MS/s write. 

Thanks all