User Manual

SCSI Commands Reference Manual, Rev. J 155

www.seagate.com Direct Access Block commands (SPC-5 and SBC-4)

3.22 READ CAPACITY (10) command

3.22.1 READ CAPACITY (10) overview

The READ CAPACITY (10) command (see table 119) requests that the device server transfer 8 bytes of parameter data describing the capacity

and medium format of the direct-access block device to the data-in buffer. This command may be processed as if it has a HEAD OF QUEUE task

attribute. If the logical unit supports protection information, the application client should use the READ CAPACITY (16) command instead of the

READ CAPACITY (10) command.

For the definition of the LOGICAL BLOCK ADDRESS field see 2.2.3.

LOGICAL BLOCK ADDRESS field

This field has been declared obsolete by the T10 committee. However, it is included because it may be implemented on some products.

The LOGICAL BLOCK ADDRESS field shall be set to zero if the PMI bit is set to zero. If the PMI bit is set to zero and the LOGICAL BLOCK ADDRESS

field is not set to zero, the device server shall terminate the command with CHECK CONDITION status with the sense key set to ILLEGAL

REQUEST and the additional sense code set to INVALID FIELD IN CDB.

PMI (Partial Medium Indicator) bit

This bit has been declared obsolete by the T10 committee. However, it is included because it may be implemented on some products.

0 A partial medium indicator (PMI) bit set to zero specifies that the device server return information on the last logical block on the

direct-access block device.

1 A PMI bit set to one specifies that the device server return information on the last logical block after that specified in the LOGICAL BLOCK

ADDRESS field before a substantial vendor-specific delay in data transfer may be encountered.

This function is intended to assist storage management software in determining whether there is sufficient space starting with the logical

block address specified in the CDB to contain a frequently accessed data structure (e.g., a file directory or file index) without incurring an extra

delay.

Table 119 READ CAPACITY (10) command

Bit

Byte

7 6 5 4 3 2 1 0

OPERATION CODE (25h)

Reserved Obsolete

(MSB)

LOGICAL BLOCK ADDRESS (Obsolete)

. . .

(LSB)

Reserved

PMI

(Obsolete)

CONTROL