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Chapter 8 SCSI Commands
8.18.2. Element reservation
Reservation Identification provides a means for the host to reserve each
element. Reservation Identification is used by the RELEASE command when
releasing the reservation.
When the Element bit is 1, the autoloader performs reservation request
processing as follows.
a) Verifies that the Element List includes valid Element Addresses. If an
Element Address is an invalid internal autoloader address, the command is
terminated with a CHECK CONDITION status. The Sense Key is
ILLEGAL REQUEST and ASC/ASCQ is INVALID ELEMENT
ADDRESS. Check that no Element in the Element List overlaps with
another Element List. If an overlap is discovered, the command is terminated
with a CHECK CONDITION status. The Sense Key is ILLEGAL
REQUEST and ASC/ASCQ is INVALID ELEMENT ADDRESS.
b) If a requested reservation does not conflict with one already requested, the
specified element is reserved until the reservation is released. Release of the
reservation occurs as a result of:
1) Issue of a valid RELEASE command by the host that issued the
RESERVE command.
2) Issue of a BUS RESET message by any host.
3) A hard reset.
4) Power on cycle.
If one of the last three conditions occurs, a CHECK CONDITION status is
returned to each host in response to the subsequent command and the
command is terminated. The Sense Key is UNIT ATTENTION.
c) If a reservation conflicts with an already established reservation that, a
RESERVATION CONFLICT status is returned and the command is
terminated.
The size of the Element List is specified by the Element List Length parameter.
The Element List, as shown in table 8.18.2.1, consists of 0 or a plurality of
Descriptors. Each Element List Descriptor consists of a specified Element
Address and the number of consecutive elements starting from that address. A
number of Elements of 0 indicates that the Element List extends consecutively
from the specified Element Address to the last Element Address in the unit.
Table 8.18.2.1 : Data format of element list descriptors
If a host issues a RESERVE command in respect of an element already reserved
by a different host, the command is terminated with RESERVATION
CONFLICT status. When a RESERVATION CONFLICT is issued, absolutely
no processing whatsoever of the command performed.
Bit
Byte
7
6
5
4
3
2
1
0
0
Reserved
1
2
(MSB)
Number of elements
3
(LSB)
4
(MSB)
Element address
5
(LSB)
