Yes, I think I do want to create partitions. My expectation is to create a mapping based on one or more raw physical device (luns). There are a number features I would like implement behind my mapping target driver. My understanding is that I can treat the mapping (the target device) as if it were a raw disk and that I can format it as appropriate for whatever workload will use it.
For instance... I need to present a device (it would appear to the OS as a raw block device) composed of ranges of blocks from different devices - spinning media, ssd, PCIe flash, etc. My target driver can guarantee a QOS (throughput, latency, combo) and it will service read requests across the range of physical media comprising the target.
This target device would appear to the OS as a block device. The workload that uses the device might require a filesystem on it, so I need to mount a FS.