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ESX server - VMWare Raw device mapping on Dell MD1000?

I just set up VMware ESX server 3.5 on a test server with a Dell MD1000 direct attached storage system. IT is attached to a dell perc 6 raid controller card. The ESX server OS is loaded on the the local server SCSI drives. (nothing is using the MD1000 yet)  VMware also can see the MD1000. It will allow me to add storage and format it when I try. The plan was to run 3 Windows 2003 Virtual machines on the VMware server and have them utilize raw device mapping to partitions on the MD1000 so I can have great disk performance for an intense SQL app. If I try and add a disk to one of the Virtual machines, the option to select raw device mappings for the disk is greayed out. Is it not posible to use an Dell MD1000 direct attached storage unit for raw device mapping disks in my Virtual machines? Would I be able to do this with an MD3000?  
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We originally though performance would be improved but reading through the various forums and seeing some others stats showed that raw vs vmdk performance was very much similar when viewed through the host machine.

this thread had some interesting results. http://communities.vmware.com/thread/73745
Sorry I didn't put all these in one answer but I couldn't find them all in one go as it was a while ago: anyway this is a document from VMware with performance stats shown for RDM and VMFS.  http://www.vmware.com/files/pdf/performance_char_vmfs_rdm.pdf
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Thanks gump103, The first document you linked to mentions that some direct access raid devices will not allow Raw Device mapping.  I confirmed this with Dell. This limitation is for both the Dell power vault  MD1000 and MD3000. The ISCSI solution (MD3000i) will allow this.
Thanks