Overview
ISO/IEC 14776-412:2006 - Information technology - Small Computer System Interface (SCSI) - Part 412: Architecture Model‑2 (SAM‑2) defines the SCSI architecture model and common behaviors for SCSI devices. The standard describes how SCSI implements a peer‑to‑peer I/O bus (bus width options noted in the scope are 8 or 16), the distributed client‑server service model, device and port abstractions, and the expected lifecycles for commands, tasks and task management functions. It is foundational for ensuring consistent SCSI device behavior and interoperability.
Key Topics and Requirements
- SCSI architecture and models
- Distributed service model, client‑server model and structural model
- SCSI domain and service delivery subsystem behaviors
- Device, port and naming conventions
- Definitions for initiator, target, target/initiator devices, ports, and SCSI names
- Multiple‑port device models and views for initiators/targets
- Logical units and addressing
- Logical unit concepts, LUN formats and addressing methods (single‑level, eight‑byte, extended, well‑known)
- Command and data transfer model
- Execute Command semantics, Command Descriptor Block (CDB) format, OPERATION CODE and CONTROL byte considerations
- Data‑In / Data‑Out transfer services and request/response ordering
- Status, sense data and exception handling
- Status codes, precedence rules, autosense and asynchronous event reporting
- Handling of contingency conditions such as Contingent Allegiance (CA) and Auto Contingent Allegiance (ACA)
- Tasks and task management
- Task object model, tags, task lifetimes, abort/clear/reset functions, task management protocol services
- Task set management
- Task states, events, and mechanisms for controlling and synchronizing task sets across initiators/targets
Applications and Who Uses This Standard
- Storage device vendors and firmware engineers implement SCSI target/initiator behavior, multi‑port support and LUN addressing.
- System architects and OS developers use SAM‑2 to ensure correct command processing, task management and error handling.
- SAN/NAS integrators and storage array designers rely on the architecture model for interoperability and multi‑host environments.
- Compliance testers and QA teams reference the standard for conformance testing and interoperability validation between SCSI components.
Related Standards
- SAM‑2 is part of the broader ISO/IEC 14776 SCSI family and complements SCSI command‑set and transport specifications (command standards, transport protocols and physical layer documents) that together define full SCSI implementations.
Keywords: ISO/IEC 14776-412:2006, SAM-2, SCSI architecture model, SCSI devices, logical unit numbers, CDB, task management, SCSI command model, SCSI interoperability.
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