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4.3 SCSI Commands
C156-E224-01EN 4-25
4.3.7 RESERVE command
Table 4.39 RESERVE command
Bit
Byte
76543210
0 Operation Code (16h)
1LUN Reserved
2-5 Reserved
As with the RELEASE command (explained next), the RESERVE command
controls exclusive access to the logical unit (ODD) in a multi-initiator
environment. The ODD is reserved for another SCSI device by the INIT that
issues this command.
Any values specified for CDB bytes 1 to 5 are ignored. However, INIT should
specify 00h for these bytes.
The RESERVE command reserves the entire ODD (logical unit) for a specific
SCSI device. The ODD reserved by this command remains reserved until one of
the following conditions is met:
• The RELEASE command is issued by the INIT that issued the RESERVE
command.
• A BUS DEVICE RESET message is issued by an INIT.
• A RESET condition occurs.
• The ODD power is turned off and on again.
While an ODD is reserved for a SCSI device, an INIT having no "reservation
authority" for the ODD might issue this command. If so, the command ends with
RESERVATION CONFLICT status.
After ODD reservation is established, any commands, other than the INQUIRY,
REQUEST SENSE, and RELEASE commands, issued by an INIT other than the
SCSI device that reserved the ODD are rejected. The RESERVATION
CONFLICT status is reported to the INIT that issued the command. The
INQUIRY and REQUEST SENSE commands are executed normally even while
the ODD is reserved for another SCSI device. The RELEASE command ends
with GOOD status, but any RELEASE command issued by a SCSI device having
no reservation authority for the applicable ODD is ignored.