ESXi 5.1 SSD guest write speed very slow

I have installed ESXi 5.1 on my server.

And machine has 4x vertex 256GB SSD drives, wich on drive is hot sphere. (RAID 5)

I have installed Windows 2011 SBS

There i downloaded a AS SSD Benchmark and HD speed recomendnd in (http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006821)for disk speed testing.

It says Seq 900MB/s for read, thats ok

But only 34.03 to 60MB/s for Write, that is really slow. i Cant understand what seems to be the problem.

here some pictures for the result

VM settings

VM performance graphc