Just a quick update. I was disappointed with disk performance in ESXi. I was also worried whether my controller was working properly with my motherboard. To verify HW compatibility I did a quick Win7 installation on my WD10EARS disks in RAID1 my 3ware 9690SA controller.
The combination performed surprisingly well with with Win7.
After booting ESXi again, I removed the win partitions with fdisk and added the datastore again(ESXi creating the new partitions).
After moving the VMs to the datastore I feel that everything working quite well, much better than before. Internal copying from datastore-datastore is reasonably quick and my virtual machines are working fine.
Maybe the reformat aligned the filesystems to the 4096byte block borders(even if it looked OK before reformat).
I found a really good document describing file system alignment.http://www.citrix.com/site/resources/dy ... nments.pdf