IBM TotalStorage 3494 Tape Library, Operator'S Manual

Page: 115 / 605

Command Priorities in the Queue
The Library Manager manages the operations queue with a set of priority levels.
The Library Manager places operation requests in the queue in priorities from 0–9.
A command priority of 0 is the highest priority, and a command priority of 9 is the
lowest priority. The priorities are established so that mount requests take
precedence over any other operation, except for operations that must be executed
on a priority basis. Therefore, priority level 0 is reserved for internally generated
operations, while host requests start with priority level 1.
Higher priority operations are taken from the queue first. Within a priority level,
operations are taken first-in, first-out (FIFO). The order may be shuffled if
commands are requeued because something, such as an I/O station, may be busy.
Priority Levels
Table 9 shows the priority levels, the operations in each level, and the operations
that you can promote to priority 2. The highest priority to which you can promote
a queued operation is priority 2.
Note: If a priority 3 operation is in the queue for a specified period of time, it is
promoted automatically to a priority 2. This prevents higher priority
operations from “blocking out” priority 3 mounts.
Table 9. Command Queue Priorities
Priority Operations Promotable
0 Inventory update —
1
v Mount from input station operations
v Mount cleaner cartridge
v Export
v Import
—
2
v
Promoted by operator
v Logical Mount - category or specific
—
3
v
Mount specific volser
v
Mount from category
Yes
4
v Move cartridge from input station
v Unlabeled tape operations
v Eject volser
Yes
5 Audit volser Yes
6 Reserved —
7 Demount Yes
8 Reserved —
9 Offline command —
For details on “Mount Operations” on page 90, “Demount Operations” on page 91,
and “Audit Operations” on page 91, see “Host-Initiated Operations” on page 90.
Chapter 3. Operational Characteristics
89