Seagate Serial Attached SCSI 接口手册

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"Serial Attached SCSI (SAS) 接口手册是Seagate Technology, Inc.对其实现的串行连接SCSI（小型计算机系统接口）的详细描述，适用于Seagate制造的硬盘。此接口与SCSI接口规范兼容，被分类为'智能'周边设备。" 本文档是Seagate公司于2009年12月发布的，修订版本为C，产品手册编号为100293071，主要涵盖了Serial Attached SCSI (SAS)接口的相关技术细节和使用方法。 Serial Attached SCSI (SAS)是一种高性能的存储协议，用于连接硬盘驱动器和其他存储设备。相较于传统的并行SCSI，SAS采用串行连接方式，提供了更高的数据传输速度和更远的数据传输距离，同时保持了与现有SCSI生态系统的兼容性。在1.2.2章节中，提到该SAS接口是基于以下适用的SCSI接口规范： 1. 它与SCSI接口规范兼容，这意味着SAS驱动器可以与支持这些规范的系统和控制器无缝集成。 2. SAS接口的设计还考虑到了其他参考标准，可能包括SCSI命令集、电气接口规定、物理层要求等，确保其在各种环境中都能稳定工作。 1.3章节概述了SAS接口的一般特性： 1.3.1 引言部分可能介绍SAS接口的基本概念，包括其设计目标、优势和相对于其他存储接口（如ATA、SATA）的改进之处。它可能会阐述SAS如何通过点对点连接实现更高效的数据传输，以及其扩展能力，能够支持SAS域内的级联和设备扩展。尽管具体内容未提供，但可以推测手册会深入讨论以下方面： - SAS接口的物理层（PHY）和协议层的详细规格，包括信号速率、电缆类型和长度限制。 - SAS驱动器的“智能”特性，可能涉及自我监测、分析和报告技术(SMART)，以及设备健康状态监控。 - SAS的拓扑结构，如背板、扩展器和交换机的使用，以构建大规模存储解决方案。 - SAS与SATA的互操作性，允许SAS环境包含SATA硬盘以降低成本。 - SAS命令集和协议栈的详细信息，这对于驱动器的软件开发和系统集成至关重要。 - 配置和故障排查指南，帮助用户正确安装和维护SAS设备。这份SAS接口手册是针对系统管理员、硬件工程师、存储解决方案设计师以及需要理解和操作SAS设备的专业人士的宝贵资源，提供了全面的技术信息和实践指导。

4 Serial Attached SCSI (SAS) Interface Manual, Rev. C

1.3 General interface description

This SAS Interface Manual describes the Seagate Technology, Inc. subset of the Serial Attached SCSI (Small

Computer Systems Interface) as implemented on the Seagate-built drives. The interface is compatible with the

SCSI Interface Specifications listed in 1.2.2. The drives covered by this product manual are classified as “Intel-

ligent” peripherals.

1.3.1 Introduction to Serial Attached SCSI Interface (SAS)

The SAS interface provides several advantages over Parallel SCSI. Parallel SCSI has reached a practical

maximum transfer rate of 320 MB/sec. Parallel SCSI is limited to a maximum of 16 devices connected to the

bus, one of which must be a host bus adapter. Fibre Channel (FC) allows SCSI to be transmitted in a serial

manner using frames, rather than on a parallel bus. It allows up to 127 devices to be addressed on fibre optic

cable, or copper conductors. FC devices are connected in a loop and arbitrate for control of the loop, using

fibre optic cable devices may be physically separated by 10km of cable. Parallel ATA (PATA) is limited to a

maximum of two devices per host adapter, lower data transfer rates, and is not considered intelligent, there-

fore, not well suited for enterprise environments. Serial ATA (SATA) increases the data transfer rate but is lim-

ited in addressing, and cable length, and intelligence. SATA uses small form cables and connectors to transfer

data at up 300 MB/sec, with the standard allowing transmission of up to 600 MB/sec. Currently SATA is a point-

to-point connection inside the computer’s system unit, with a maximum length of 18 inches. External SATA is in

the development stage.

SAS combines the intelligence of SCSI with the physical transport layer. This scheme allows the intelligence of

SCSI to be transferred on a serial cable similar to SATA. Data is transfer in frames, like Fibre Channel. The ini-

tial data transfer rate for SAS was 300 MB/sec. with the SAS-2 standard allowing up to 600 MB/sec. SAS pro-

vides for full duplex operation, at 300 MB/sec. it is possible to attain 600 MB/sec. per pathway. SAS is a point

to point connection as is SATA, Expanders are used to increase the number of devices that may be connected.

Unlike Parallel SCSI and Fibre Channel SAS drives and Serial ATA drives may be attached to the same

expander.

1.3.2 The SAS interface

The Seagate SAS interface described herein consists of a dual ported SAS bidirectional links. The SCSI inter-

face supports multiple initiators, disconnect/reconnect, self-configuring host software, automatic features that

relieve the host from the necessity of knowing the physical architecture of the target (logical block addressing

is used), and some other miscellaneous features.

Unless specified otherwise in the individual drive’s product manual, the drive is always a SAS target port, and

never a SAS initiator port. For certain commands, which may or may not be supported by a particular drive

model, the drive must act as a SAS initiator port, but does not otherwise do so. For purposes of this specifica-

tion, “drive” may be substituted for the word “target” wherever “target” appears.

In the event of a conflict between this document and ANSI SCSI documents, the requirements of the ANSI doc-

uments shall apply.

In figure 2, it can be seen that several “application clients” from a single initiator may have one or more tasks in

queue with several “device servers” in a single target. A drive could be a SCSI target port or it could be one of

the device servers as part of some larger entity. When reading the description, one needs to be able to put the

drive of interest in the proper context in terms of what is shown in figure 2. For a proper understanding of the

operation of the SCSI protocol, the terms in the SCSI architectural model as described in SAM-4 should be

Print Date:2010-Jan-13 11:56:37 CST Released; Prod Rel; C; 100293071 Seagate Confidential

6 Serial Attached SCSI (SAS) Interface Manual, Rev. C

1.3.3 Glossary

8b 10b coding—A coding scheme that represents an 8-bit data byte as a 10-bit character.

aborted command—A SCSI command that has been ended by aborting the task created to execute it.

ACA—Auto Contingent Allegiance (see below).

ACA command—A command performed by a task with the ACA attribute. For additional information about the

ACA command, refer to the Seagate SCSI Commands Reference Manual.

ACK—Acknowledge primitive that specifies the positive acknowledgement of an SSP frame.

application client—An object that is the source of SCSI commands. An object in this sense is not a tangible

piece of hardware, but may be a single numeric parameter, such as a logical unit number, or a complex entity

that performs a set of operations or services on behalf of another object (see SAM-4).

auto contingent allegiance—One of the conditions of a task set following the return of a CHECK CONDITION

status.

big-endian: A format for storage or transmission of binary data in which the most significant byte appears first.

In a multi-byte value, the byte containing the most significant bit is stored in the lowest memory address and

transmitted first and the byte containing the least significant bit is stored in the highest memory address and

transmitted last (e.g., for the value 0080h, the byte containing 00h is stored in the lowest memory address and

the byte containing 80h is stored in the highest memory address).

blocked (task state)—The state of a task that is prevented from completing due to an ACA condition.

broadcast primitive processor (BPP)—An object within an expander function that manages broadcast primi-

tives.

burst time—The part of an OOB signal (see 4.5) where ALIGN primitives (see 5.2.5.1) are being transmitted.

byte—A sequence of eight contiguous bits considered as a unit.

call—The act of invoking a procedure.

character—A sequence of ten contiguous bits considered as a unit. A byte is encoded as a character using

8b10b coding.

client-server—A relationship established between a pair of distributed objects where one (the client) requests

the other (the server) to perform some operation or unit of work on the client’s behalf (see SAM-4).

Client—An object that requests a service from a server.

command—A request describing a unit of work to be performed by a device server.

command descriptor block (CDB)—A structure used to communicate a command from a SCSI application

client to a SCSI device server. See SAM-4.

common SSC transmit clock: An implementation that employs a single transmit clock for multiple transmitter

devices and enables or disables SSC(see 3.6.6) on the transmit clock signal to all transmitter devices in com-

mon rather than allowing each transmitter device to independently control SSC.

compliance point: An interoperability point where interoperability specifications are met. See .

compliant jitter tolerance pattern (CJTPAT): A test pattern for jitter testing. See 3.6.5.6.

completed command—A command that has ended by returning a status and service response of Task Com-

plete or Linked Command Complete.

completed task—A task that has ended by returning a status and service response of Task Complete. The

actual events comprising the Task Complete response are protocol specific.

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Serial Attached SCSI (SAS) Interface Manual, Rev. C 7

configurable expander device—An expander device that contains an expander route table that is configured

with expander route entries.

confirmation—A response returned to an object, which signals the completion of a service request.

confirmed service—A service available at the protocol service interface, which requires confirmation of com-

pletion. The confirmed service consists of the request and confirmation steps and optionally the indication and

response steps.

connection—A temporary association between a SAS initiator port and a SAS target port.

connection rate—The effective rate of dwords through the pathway between a SAS initiator phy and a SAS

target phy, established through the connection request.

control character (Kxx.y)—A character that does not represent a byte of data.

control mode page—The mode page that identifies the settings of several device server behaviors that may

be of interest to an application client or may be changed by an application client. The complete definition of the

Control mode page is found in the Seagate SCSI Commands Reference Manual.

current task—A task that is in the process of sending messages, sending status, transferring data, or transfer-

ring command data to or from the initiator.

cyclic redundancy check (CRC)—An error checking mechanism that checks data integrity by computing a

polynomial algorithm based checksum (see 5.5).

data character (Dxx.y)—A character representing a byte of data.

data dword—A dword that starts with a Dxx.y (data character).

D.C. idle—A differential signal level that is nominally 0 V(P-P).

deadlock—A condition in which two or more processes (e.g., connection requests) are waiting on each other

to complete, resulting in none of the processes completing.

destination device—The SCSI device to which a service delivery transaction is addressed. See source

device.

deterministic jitter—Jitter with a non-Gaussian probability density function. Deterministic jitter is always

bounded in amplitude and has specific causes. Four kinds of deterministic jitter are identified: duty cycle distor-

tion, data dependent, sinusoidal, and uncorrelated (to the data) bounded. Deterministic jitter is characterized

by its bounded, peak-to-peak value.

device name— A worldwide unique name for a device within a transport protocol.

device server—An object within a SAS target device that processes SCSI tasks (see SAM-4).

device service request—A request, submitted by an application client, conveying a SCSI command to a

device server.

device service response—The response returned to an application client by a device server on completion of

a SCSI command.

differential—A signalling alternative that employs differential (two complementary signals) drivers and receiv-

ers to improve signal-to-noise ratios and increase maximum cable lengths.

direct current (D.C.)—The non-A.C. component of a signal. In this, all frequency components below 100 kHz.

discover process—The algorithm used by a management application client to configure the SAS domain.

See SAS-2.

disparity—The difference between the number of ones and zeros in a character.

Print Date:2010-Jan-13 11:56:37 CST Released; Prod Rel; C; 100293071 Seagate Confidential

8 Serial Attached SCSI (SAS) Interface Manual, Rev. C

domain—A SAS domain, a SCSI domain, or an ATA domain.

dword—A sequence of four contiguous bytes or four contiguous characters considered as a unit. The meaning

depends on the context (e.g., when discussing the bits being transmitted over a physical link, dword represents

four characters (i.e., 40 bits). When discussing the contents of a frame after 10b8b decoding (see 4.2), dword

represents four bytes (i.e., 32 bits)).

dword synchronization—Detection of an incoming stream of dwords from a physical link by a phy.

expander connection manager (ECM)—An object within an expander function that manages routing.

expander connection router (ECR)—The portion of an expander function that routes messages between

expander phys.

enabled (task state)—The state of a task that may complete at any time. Alternatively, the state of a task that

is waiting to receive the next command in a series of linked commands.

end device—A SAS device that is not contained within an expander device.

ended command—A command that has completed or aborted.

event notification—A message passed from the transport layer to the application layer notifying the applica-

tion layer that a SCSI event has occurred. See SAM-4.

exception condition—Any event that causes a SCSI device to enter an auto contingent allegiance or contin-

gent allegiance condition.

expander device—A device that is part of the service delivery subsystem and facilitates communication

between SAS devices.

expander function—An object within an expander device that contains an expander connection manager,

expander connection router, and broadcast primitive processor.

expander phy—A phy in an expander device that interfaces to a service delivery subsystem.

expander port—An expander device object that interfaces to the service delivery subsystem and to SAS ports

in other devices.

expander route entry—A routed SAS address and an enable/disable bit in an expander route table.

expander route index—A value used in combination with a phy identifier to select an expander route entry in

an expander route table.

faulted initiator—The initiator to which a Command Terminated or CHECK CONDITION status was returned.

faulted task set—A task set that contained a faulting task.

faulting command—A command that completed with a status of Check Condition or Command Terminated.

faulting task—A task that has completed with a status of Check Condition or Command Terminated.

field—A group of one or more contiguous bits.

frame—A sequence of data dwords between a start of frame primitive (e.g., SOF, SOAF, or SATA_SOF) and

an end of frame primitive (e.g., EOF, EOAF, or SATA_EOF).

hard reset—A SAS device or expander device action in response to a reset event.

Hard reset sequence—A sequence that causes a hard reset.

hardware maximum physical link rate—The maximum physical link rate capability of a phy.

hardware minimum physical link rate—The minimum physical link rate capability of a phy.

Print Date:2010-Jan-13 11:56:37 CST Released; Prod Rel; C; 100293071 Seagate Confidential

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