def createDiskSpec(scsiKey,diskKey,unitNumber,diskSize,diskMode,datastore):
"""
Define a virtual disk spec
"""
diskSpec = VirtualDeviceConfigSpec()
diskSpec.setOperation(VirtualDeviceConfigSpecOperation.add)
diskSpec.setFileOperation(VirtualDeviceConfigSpecFileOperation.create)
vd = VirtualDisk()
vd.setKey(diskKey)
vd.setCapacityInKB(diskSize)
vd.setUnitNumber(unitNumber)
vd.setControllerKey(scsiKey)
diskfileBacking = VirtualDiskFlatVer2BackingInfo()
fileName = "["+datastore+"]"
diskfileBacking.setFileName(fileName)
diskfileBacking.setDiskMode(diskMode)
diskfileBacking.setThinProvisioned(True)
vd.setBacking(diskfileBacking)
diskSpec.setDevice(vd)
return diskSpec
