Performance benchmarking shows that skipping the raw format blockdev improves I/O performance. On an Optane NVMe drive where small improvements are most noticeable it reduces I/O latency by ~300 ns and increases IOPS by 3,000.

The raw format driver simply passes requests to the protocol driver (raw-posix, iscsi, etc). Omitting it does not affect disk I/O except that it increases performance slightly.

Note that the raw format driver can be used to expose a subset of the underlying storage using the offset=/size= parameters. In this case the raw format driver is necessary and cannot be omitted.

Please omit the raw format blockdev when possible.