command-descriptor-block · shipping · also CDB, SCSI CDB

Command descriptor block (CDB)

A command descriptor block (CDB) is the byte-encoded description of a SCSI command.

Related Observatory article: Command descriptor block (CDB) on hesela.com

Command and data: The CDB identifies a command and is distinct from its associated data payload. Common fixed-length formats are 6, 10, 12 and 16 bytes; the operation and command set determine the layout. [1] [2]

Interpretation: Decode the command using the applicable device command set, such as SBC for block devices or SSC for sequential-access devices. A shared SCSI transport does not make their operations interchangeable. [3]

Relations

related
SCSI, SCSI initiator and target, Logical unit number (LUN), SCSI CHECK CONDITION

Citations

  1. SNIA dictionary: Command Descriptor Block (accessed 2026-10-20)
  2. Linux SCSI Interfaces Guide: protocol versus bus and subsystem layers (accessed 2026-10-20)
  3. T10: SCSI standards architecture and command families (accessed 2026-10-20)
Sources & caveats
  • The listed fixed lengths are examples, not an exhaustive limit on SCSI command formats.

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Hesela team. Command descriptor block (CDB). Hesela. 2026-10-20. https://hesela.dev/terms/command-descriptor-block/