Third Party Reservation; Superseding Reservations; Reservations - Seagate SCSI Interface Product Manual

SCSI Interface Product Manual, Rev. J
5.35.3

Third Party Reservation

The third party reservation option for the Reserve command allows an initiator to reserve a logical unit for
another SCSI device. If the drive supports third party reserve command, the drive also implements the third
party release option (see Section 5.31.3). This feature is intended for use in multiple-initiator systems that use
the Copy command. Check individual drive's Product Manual, Volume 1, to see if the drive supports the third
party reservation option.
If the third party (3rdPty) bit is zero, 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 third party device
ID field. The drive shall preserve the reservation until it is superseded by another valid Reserve command from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 Bus Device Reset mes-
sage from any initiator, or a "hard" Reset condition. The drive shall ignore any attempt to release the reserva-
tion made by any other initiator.
5.35.4

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 shall release the previous reservation state
when the new reservation request is granted. The previous reservation shall not be modified if the new reser-
vation request cannot be granted.
5.35.5

Reservations

Reservations may be used to allow a device server to execute commands from a selected set of initiators. The
device server rejects any commands from initiators outside the selected set by uniquely identifying initiators
using protocol specific mechanisms.
Application clients may add or remove initiators from the selected set using reservation commands. If the appli-
cation clients do not cooperate in the reservation protocol, data may be unexpectedly modified and deadlock
conditions may occur.
The general description of reservations involves two groups of considerations:
a. the type of reservation established, and
b. the method used to establish, rescind, and manage the reservation.
Table 159: Reservation commands
Operation
Code Command Name
16h Reserve (6)
56h Reserve (10)
17h Release (6)
57h Release (10)
5Eh Persistent Reserve In
5Fh Persistent Reserve Out 5.16
The subject of Reservations is large and detailed, and therefore not covered entirely in this manual. It is recom-
mended that the reader refer to ANSI document T10/1157-D, sections 5.3, 7.11, 7.12, 7.16, 7.17, 7.21, and
7.22, for a greater understanding of and details pertaining to the reservation process as needed for design pur-
poses.
Section Page
5.35 200
5.36 202
5.31 187
5.32 188
5.15 153
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