5.17PERSISTENT RESERVATION OUT Command (5Fh)

The PERSISTENT RESERVATION OUT command is a 10-byte command used to reserve a logical unit or an extent within a logical unit for the exclusive or shared use by an initiator. The command is used in conjunction with the PERSISTENT RESERVATION IN command; it is not used with the RESERVE and RELEASE commands.

Persistent reservations conflict with reservations made via the RESERVE command. Initiators that perform PERSISTENT RESERVATION OUT actions are identified by a reservation key assigned by the application client. The client may use the PERSISTENT RESERVATION IN command to identify which other initiators within a system hold conflicting or invalid persistent reservations and use the PERSISTENT RESERVATION OUT command to preempt those reservations if necessary.

Note that since persistent reservations are not reset by the TARGET RESET task management function or other global actions, they can be used to enact device sharing among multiple initiators. The PERSISTENT RESERVATION OUT and PERSISTENT RESERVATION IN commands provide the means for resolving contentions in multiple-initiator systems with multiple port target. By using the reservation key to identify persistent reservations, it is possible to determine which ports hold conflicting persistent reservations and to take over such reservations from failing or “greedy” initiators.

illustrates the format of the PERSISTENT RESERVATION OUT command. Table 5-113explains the data fields of the command.

Table 5-112PERSISTENT RESERVATION OUT Command Descriptor Block-Data Format

Bit

7

6

 

5

 

4

 

3

 

2

 

1

0

Byte

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

 

 

 

 

Operation

Code (5Fh)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

Reserved

 

 

 

 

Service Action

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2

 

Scope

 

 

 

 

 

 

Type

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3 - 6

 

 

 

 

 

 

Reserved

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7 – 8

 

 

 

 

 

 

(MSB)

 

 

 

 

 

 

 

 

Parameter List Length (18h)

 

 

 

 

 

 

 

 

 

 

 

(LSB)

 

 

 

 

9

 

 

 

 

 

 

Control

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Maxtor Atlas 10K V

5-81