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300 Fibre Channel Interface Manual, Rev. D
12.40.1 Logical unit reservation
When the Extent bit is zero, this command requests the entire disc drive to be reserved for exclusive use of the
initiator until the reservation is superseded by another valid Reserve command from the initiator that made the
reservation, released by a Release command from the same initiator, by a LIP Reset from any initiator, or be a
hard Reset condition. A logical unit reservation is not granted if the logical unit is reserved by another initiator.
It is permissible for an initiator to reserve a logical unit that is currently reserved by the initiator. If the Extent bit
is zero (0), the Reservation Identification and the Extent List Length are ignored. If the Extent bit is a 1, the disc
drive generates Check Condition status and sets the sense key to Illegal Request.
If, after honoring the reservation, any other initiator subsequently attempts to perform a command other than a
Release command (which will be ignored), or an Inquiry command (which will be executed), or a Request
Sense command (which will be executed), the command is rejected with Reservation Conflict status.
12.40.2 Third-party reservation
The third-party reservation option of the Reserve command allows an initiator to reserve a logical unit for
another SCSI device. If the drive supports the third-party Reserve command, the disc drive also implements
the third-party Release option (see Section 12.35). This feature is intended for use in multiple-initiator systems
that use the Copy command.
If the third-party (3rdPty) bit is zero (0), the third-party reservation option is not requested. If the 3rdPty bit is
one, the Reserve command reserves the specified logical unit for the SCSI device specified in the parameter
list. The disc drive preserves the reservation until it is superseded by another valid Reserve command from the
initiator which made the reservation or until it is released by the same initiator, by a LIP Reset from any initiator,
or a hard Reset condition. The disc drive ignores any attempt to release the reservation made by any other ini-
tiator.
12.40.3 Superseding reservations
An initiator which holds a current reservation may modify that reservation by issuing another Reserve com-
mand to the same logical unit. The superseding Reserve command releases the previous reservation state
when the new reservation request is granted. The previous reservation is not modified if the new reservation
request cannot be granted.