IBM Magstar 3494 Command Priorities in the Queue, Priority Levels, Priority Operations Promotable

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 ®rst. Within a priority level, operations are taken ®rst-in ®rst-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 speci®ed period of time, it is

automatically promoted to a priority 2. This prevents priority 3 mounts from being ªblocked outº by higher priority operations.

Table 4. Command Queue Priorities

Priority	Operations		Promotable
0	Inventory update		Ð
1	v	Mount from category	Ð
	v Mount from input station operations
	v	Mount cleaner cartridge
	v	Export
	v	Import
2	v	Promoted by operator	Ð
	v Logical Mount - category or speci®c
3	Mount speci®c volser		Yes
4	v Move cartridge from input station		Yes
	v	Unlabeled tape operations
	v	Eject volser
5	Audit volser		Yes
6	Reserved		Ð
7	Demount		Yes
8	Reserved		Ð
9	Offline command		Ð

For details on Mount Operations, Demount Operations, and Audit Operations, see ªHost-Initiated Operationsº on page 55.

54Magstar 3494 Tape Library Operator Guide