Overview
ISO/IEC 14776-262:2017 - "Information technology - Small Computer System Interface (SCSI) - Part 262: SAS Protocol Layer - 2 (SPL-2)" specifies the protocol-layer model and command set extensions used together with the SCSI Primary Command Set (SPC‑4) to support operation of SCSI direct‑access block devices (for example, hard disk drives). The standard defines behavioral models, state machines, naming and addressing, and the expander/port mechanisms required for reliable Serial Attached SCSI (SAS) operation at the protocol layer.
Key topics and technical requirements
- Architecture and layering: Defines the SAS protocol layer concepts, physical links (phys), logical links, narrow/wide ports, and how the protocol integrates with SPC‑4 for block device commands.
- State machines and data paths: Specifies transmit and receive data‑path state machines and their transitions for robust command delivery and error handling.
- Expander device model: Detailed model of expander devices including expander ports, routing, connection manager (ECM), connection router (ECR), and broadcast propagation processor (BPP).
- Discovery and configuration: Procedures for topology discovery, routing table construction, multiplexing enablement, and expander configuration options.
- Names, identifiers and addressing: Rules for SAS addresses, NAA formats, hashed addresses, port and phy identifiers, and handling of SATA devices with world wide names.
- Events and resets: Defined behaviors for hard resets, I_T nexus loss, power‑loss events and related recovery sequences.
- Zoning and security controls: Zoning mechanisms, zone groups, permission tables and how zoning affects expander routing and broadcast handling.
- Routing and topology: Expander route tables, routing attributes and methods, topology restrictions and optimization considerations.
Applications and who uses this standard
ISO/IEC 14776-262:2017 is used by:
- Firmware and hardware engineers designing SAS host bus adapters (HBAs), controllers, expanders and storage enclosure logic.
- Storage system architects and OEMs implementing SAS-based RAID arrays, JBOD enclosures and enterprise storage solutions.
- Interoperability and test teams performing compliance, conformance and interoperability testing between SAS devices.
- Integrators and data center operators implementing zoning, path management and high‑availability storage networks.
Practical benefits include consistent device behavior, predictable discovery and routing, improved interoperability, and standardized error/recovery procedures for SCSI direct‑access block devices over SAS.
Related standards
- SCSI Primary Command Set (SPC‑4) - used in conjunction with SPL‑2 for command semantics.
- Other parts of the SAS protocol family and SAS physical‑layer standards (related SPL and PHY documents) that define lower‑level signaling and additional protocol layers.
Keywords: ISO/IEC 14776-262:2017, SAS Protocol Layer 2, SPL-2, SCSI, SPC-4, SAS expander, SAS addressing, zoning, storage interoperability.
Open preview (PDF)Information technology — Small computer system interface (SCSI) — Part 262: SAS protocol layer - 2 (SPL-2)
