How to understand SAN stores data at the block level, while NAS accesses data as files?
Solution 1:
Yes, from the client, the SAN will export whole virtual disks (with a protocol like iSCSI) and the client OS has to mount it with its own filesystem logic. There should be no restrictions on the supported logics (ext4, swap, others).
A NAS will be seen as a shared directory, and file accesses are just transmitted with one of the supported protocol (CIFS, NFS). The file system logic runs in the NAS.