Chapter 5

SCSI Description

This chapter contains an overview of SCSI command and status processing and a detailed description of the commands supported by the disk drives. The SCSI command system enables the initiator to instruct the drive to perform specific functions.

In this manual, unless otherwise stated, numerical values are given in decimal. Hexadecimal numbers, such as opcodes, are always given with an “h” following, as in 5Ah except when entire data tables are in hexadecimal.

5.1Overview of the SCSI Command Descriptions

The disk drives support the SCSI-3 commands listed in Table 5-1. The command categories are sequential, normal, and immediate.

Immediate commands are processed when received by the drive. In most cases, these commands do not require drive resources, do not change the state of the drive, and bypass the command queue (unless the command is tagged).

Sequential commands execute in the order that they arrive (unless accompanied by a HEAD OF QUEUE tag) and execute to completion before a subsequent command is activated.

Normal commands are allowed to execute concurrently (with the restriction that the drive executes overlapping writes in the order received). Normal commands are usually I/O commands

Table 5-1Supported SCSI Commands

Command

Operation Code

Category

 

 

 

CHANGE DEFINITION

40h

Sequential

 

 

 

FORMAT UNIT

04h

Sequential

 

 

 

INQUIRY

12h

Immediate

 

 

 

LOG SELECT

4Ch

Sequential

 

 

 

LOG SENSE

4Dh

Sequential

 

 

 

MODE SELECT (6)

15h

Sequential

 

 

 

MODE SELECT (10)

55h

Sequential

 

 

 

MODE SENSE (6)

1Ah

Sequential

 

 

 

MODE SENSE (10)

5Ah

Sequential

 

 

 

PERSISTENT RESERVATION IN

5Eh

Sequential

 

 

 

Maxtor Atlas 10K V

5-1

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Image 59
Maxtor 10K V manual Overview of the Scsi Command Descriptions