IBM Tape Library Magstar 3494 - Manual (Page 76)

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 through
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 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 get requeued because something, such as an I/O station, may be busy).
Priority Levels
Table 4 shows the priority levels, the operations in each level, and the operations
that the operator can promote to priority 2. The highest priority that an operator can
promote a queued operation is Level 2.
Note: If a priority 3 operation is in the queue for a specified period of time, it is
automatically promoted to a priority 2. This prevents priority 3 mounts from
being “blocked out” by higher priority operations.
Table 4. Command Queue Priorities
Priority Operations Promotable
0 Inventory update —
1
v Mount from category
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 Mount specific volser 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, Demount Operations, and Audit Operations, see
“Host-Initiated Operations” on page 55.
54 Magstar 3494 Tape Library Operator Guide
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