Which protocol is primarily used for block storage access?

• A. HTTP
• B. NFS
• C. CIFS
• D. iSCSI

Answer: (D)

Block storage access requires presenting raw storage blocks (like virtual disks) to a host so they can be managed at the block level rather than as files. The protocol that does this over an IP network is iSCSI: it carries SCSI commands over TCP/IP, so a server can see remote storage as if it were a local disk. This is the typical setup for SAN environments, where storage arrays expose LUNs that hosts mount as local drives.

In contrast, HTTP is a general web transfer protocol, and both NFS and CIFS provide file-level access to shared directories and files, not raw blocks. They expose a filesystem view rather than a block device. Therefore, iSCSI best fits block storage access.