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PERSISTENT RESERVE OUT Command (5Fh) SDLT 600 SCSI Interface Guide

4-142 January 2005 81-81200-02 REV A01

4.12 PERSISTENT RESERVE OUT Command (5Fh)

PERSISTENT RESERVE OUT is a 10-byte command used to reserve a logical unit for exclusive or

shared use of an initiator. The command is used with the PERSISTENT RESERVE IN command.

Initiators that perform PERSISTENT RESERVE OUT actions are identified by a Reservation Key the

application client assigns. The application client uses the PERSISTENT RESERVE IN command to

identify which other initiators within a system hold conflicting or invalid persistent reservations and

uses the PERSISTENT RESERVE OUT command to preempt those reservations, if necessary.

Since the SCSI bus reset of TARGET RESET or other global action does not reset persistent

reservations, they can be used to enact device sharing among multiple initiators. The PERSISTENT

RESERVE OUT and PERSISTENT RESERVE IN commands provide the means for resolving

contentions in multiple-initiator systems with multiple port targets. By using the Reservation Key to

identify persistent reservations, it is possible to determine which ports hold conflicting persistent

reservations and to reclaim these reservations from failing or “greedy” initiators.

Figure 4-80 illustrates the format of the PERSISTENT RESERVE OUT command.

Figure 4-80. PERSISTENT RESERVE OUT Command Descriptor Block — Data Format

Bit

Byte

7 6 5 4 3 2 1 0

0 Operation Code (5Fh)

1 Reserved Service Action

2 Scope Type

3 – 6 Reserved

7 – 8

(MSB)

Parameter List Length (18h)

(LSB)

9 Control

SDLT 600

SCSI Interface Guide

SCSI Commands

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REV A01

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Quantum 1200 Series DAT Autochanger Betriebsanweisung Seite 184