5.5DATA Transfer Command Components

Many of the SCSI commands cause data to be transferred between the initiator and the drive. The content and characteristics of this data are command-dependent. Table 5-8 lists the information transmitted for all of the commands.

The “Length in CDB” column of Table 5-8 identifies the Command Descriptor Block field used by the drive to determine how much command-related data are to be transferred. The units (bytes or logical blocks) for the different Length fields are implied by the Length Field Name as shown in Table 5-7:

 

Table 5-7Length Fields

 

 

 

Field Name

 

Units Implied

 

 

 

 

 

 

Allocation Length

 

Bytes of data the drive is allowed to send to the initiator

 

 

 

Parameter List Length

 

Bytes of data the initiator has available for the drive

 

 

 

Transfer Length

 

Logical data sectors the initiator wants transferred or verified

 

 

 

Byte Transfer Length

 

Bytes of data the initiator wants transferred

 

 

 

The DATA OUT column in Table 5-8 lists the information passed to the drive by the initiator as part of the command. The DATA IN column lists the information sent to the initiator by the drive.

Numbers in parentheses after an item indicate the item’s length in bytes. In some cases, additional length information is communicated during the DATA phase. For example, a FORMAT UNIT Defect List Header contains a Defect List Length field that contains the total length of the Defect Descriptors that follow the Defect List Header. Table 5-8 does not include these cases.

Table 5-8DATA-Phase Command Contents

Command

Length in CDB

Data Out (To Drive)

Data In (To Initiator)

 

 

 

 

 

 

 

 

CHANGE

0

--

--

DEFINITION

 

 

 

 

 

 

 

 

 

Defect List Header

 

FORMAT UNIT

0

Initialization Pattern (6-8)

 

 

 

Defect Descriptors

 

 

 

 

 

INQUIRY

Allocation

---

Standard Inquiry or a Vital Product

Data page

 

 

 

 

 

 

 

LOG SELECT

Parameter List

--

--

(must be 0)

 

 

 

 

 

 

 

LOG SENSE

Allocation

---

Log Page

 

 

 

 

 

Parameter List

Mode Parameter Header (4

 

MODE SELECT

Block Descriptor (8

--

 

 

 

Page(s))

 

 

 

 

 

MODE SENSE

Allocation

---

Block Descriptor (8)

 

 

 

 

 

 

PERSIST. RES. IN

 

 

 

 

 

 

 

PERSIST. RES.

 

 

 

OUT

 

 

 

 

 

 

 

READ (6) (10)

Transfer

---

Data

 

 

 

 

Maxtor Atlas 10K V

5-9

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Maxtor 10K V manual Data Transfer Command Components, 8DATA-Phase Command Contents