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Prioritized Staging and Destaging Control

IP.com Disclosure Number: IPCOM000086845D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Hart, CW: AUTHOR [+5]

Abstract

In a staging-destaging mass storage system, a large number of functions are performed at the request of various host computers (not shown). For more efficiently controlling the operation of the mass storage system, certain time consuming functions should be deferred while other functions related directly to CPU access should be performed in a prompt manner.

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Prioritized Staging and Destaging Control

In a staging-destaging mass storage system, a large number of functions are performed at the request of various host computers (not shown). For more efficiently controlling the operation of the mass storage system, certain time consuming functions should be deferred while other functions related directly to CPU access should be performed in a prompt manner.

Generally, the mass storage control includes a programmed control which operates a mass memory divided into a plurality of independent portions and a buffer memory for containing the staged data for immediate access by any host computer (not shown). Transfer of data signals from the mass memory to the buffer memory is called staging, while the reverse is termed destaging. The host computers address the data contained in the memory system by using virtual addressing to so-called virtual volumes (VV). Such virtual volumes are mounted on virtual units (logically addressed areas) in the buffer memory.

Accordingly, the following functions have top priority: acquire space in the buffer memory; relinquish space in the buffer memory; demount a virtual volume from a virtual unit contained in the buffer memory; and copy a virtual volume from the buffer memory to the mass memory, i.e., destage the data. A second-level priority includes a delayed response function mounting a virtual volume, i.e., no data transfer is yet required, copy the tables from the control, or act upon obtaining data from the mass memory to the buffer memory when such data is not in the buffer memory. The mount function merely is a logical assignment of a virtual unit to the buffer memory without allocating any memory space to such virtually mounted volume.

The lowest priority is to transfer data signals from one independent portion of the mass memory to another independent portion of the mass memory. Other priorities can be envisioned.

For each received command, the programmed control determines the proper activation priority in a priority table established in accordance with the above- described priorities. Once the priority is established, the queue control block (QCB) includes the priority designation and QCB is inserted into the proper point of a queue. Finally, the programmed control inserts the IQCB (incoming queue control block) with its associated priority indicators into a collapsing action FIFO queue within its priority subclass (1, 2 or 3).

The program control includes a program module called a QCB Queue Handler which supplies signals to a Stage Scheduler which controls the transfer of signals from the mass memory to the buffer memory via one of four queues, each queue associated with the respective independent portions of the mass memory. Each QCB includes an offset to the pointed-to QCB entry in the appropriate QCB Queue, as well as the activation priority.

The QCB Queue...