Amazon AWS vs. RackSpace Cloud Windows 2008 I/O Test

I did a basic test trying to measure the un-tuned out-of-the-box I/O performance of Rackspace Cloud instance with the HDTune utility on a Windows Server 2008 instance. According the the RS documentation their disks are local RAID10. Then I run the same utility on 8 core extra large  EBS backed EC2 instance provided by Amazon (wanted to make sure it is not an issue due to a small EC2 instance size). According to the docs EBS should provide consistent performance of a SAN regardless of the instance type.

Here are the somehow surprising results. I was expecting, that they perform somehow equal but RS is in the range of 300 MB/s whereas the EC2 instance is below 40 MB/s.

Rackspace Cloud with Windows 2008:

AWS with Windows 2008:

Interesting enough also the CPU usage is quite different: 2% only for AWS and 31% for RS.

I welcome any comments and I am aware that the tool is meant to measure disks and not RAID or SAN volumes. Still I am surprised by the huge difference. I wonder if the difference is only due to the difference of local RAID vs. SAN. Also I wonder how is the SAN attached then, since the SAN performance is still worse than my laptop disk.