IBM Magstar 3494 Command Priorities in the Queue, Priority Levels

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. Acommand 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
Table4 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.
Table4. Command Queue Priorities
Priority Operations Promotable
0 Inventory update —
1vMount from category
vMount from input station operations
vMount cleaner cartridge
vExport
vImport
—
2vPromoted by operator
vLogical Mount - category or specific
—
3 Mount specific volser Yes
4vMove cartridge from input station
vUnlabeled tape operations
vEject 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 TapeLibrary Operator Guide
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