how to boot from SCSI in Virtual Machine

hi 

i have VM's in Hyper V windows server 2012 data center edition.

i want to boot from SCSI drive for performance enhancement. 

but when i select scsi then it doesnt boot and says boot failure no boot device found.

also tried with bios settings of VM but there is no option to select boot from SCSI.

so can anyone help me how to make it happen???

how to boot from SCSI drive in VM???

thnx 

istiaq