International Business Machines Corporation

Harry O Hempy

Scott Milton Fry

Bruce E Kittinger

Charles R Kirkpatrick

Francis L Robinson

David C Cole

Phuoc D Phan

A peripheral data storage system employing a data buffer connected to a plurality of data storage devices, such as tape recorders, dynamically reallocates data buffer storage segments among the various data storage devices. A normalized elapsed-time period is established based upon the number of accesses to the data storage devices. When the number of accesses reaches a threshold the need for dynamic reallocation is examined. During the elapsed-time period the system monitors which of the allocated buffer segments have any data transfer activity at all and also measures the intensity of the activity for the respective buffer segments. In a peripheral system, the intensity is indicated by the number of channel command retries submitted to a connected host processor for the respective allocated buffer segment. Based upon the allocation status of the buffer segments and intensity of activities of the respective buffer segments, the buffer allocations are selectively reallocated among the data storage devices.

Dynamic buffer reallocation

Data transfers between respective buffer segments and data source-sinks, such as peripheral data storage devices, are scheduled as a series of transfers based upon most recent, next most recent, to the least recent usage of the buffer segments by a utilization device. A list of segments ordered by such usage is dynamically maintained. Replacement of segment allocations among devices proceeds from the least recently used, next least recently used, etc. to the most recently used segments. Therefore a single list controls replacement and read ahead (prefetch) of data from devices to the buffer and transfer of data from the buffer to the devices, all based on utilization of the buffer by the utilization device.

Scheduling device operations in a buffered peripheral subsystem

Data transfers between a host processor and a peripheral data recorder in a peripheral data storage system, such as tape recorder peripheral data storage system, are via a random-access buffer store in the peripheral data storage system and interposed between the peripheral data recorder and the host processor. A command queue storage in the peripheral data storage system stores commands received from the host processor for the peripheral data recorder. Additionally, apparatus in the peripheral data storage system form commands for transferring data between the peripheral data recorder and the buffer store without intervention of the host processor; both read transfers (data transfer from the peripheral data recorder to the host processor) and write transfers (data transfer from the host processor to the peripheral data recorder) are enabled via the formed commands.

Queuing commands in a peripheral data storage system

In a buffered data storage subsystem, data is promoted to the buffer in anticipation of a connected host using the promoted data in the near future. In a tape recorder data storage apparatus the actual position of the tape reflects the last promoted data; such actual tape position is 'inconsistent' with host operations. If the sequence of host operations continues, such inconsistency actually enhances total operations. When the subsystem detects a change or possible change in future host operations (rewind command, change in tape motion direction, etc.), detect end of file (tape mark) or a change in subsystem operations (load balance affecting drive or deallocation of buffer from drive) the data promoted to the buffer and not read by the host is erased from the buffer. The tape is moved such that upon a forward motion the tape drive would next read data on tape corresponding to the data block erased from the buffer.

Controlling buffered peripheral subsystems

Data processing workloads are balanced between a plurality of data processing units, such as control units of a peripheral system, based upon tallies of data processing delays. The workloads are arranged in work allocations, such as assignment of peripheral devices to a control unit; a separate delay tally is kept for each work allocation along with a summation of all delays in each control unit. When a tally threshold in any data processing unit is exceeded, load balance is examined. Upon a predetermined imbalance, a work allocation having a delay tally equal to a mean value of the different delay summations is transferred to a data processing unit having a lower delay summation.

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Tucson, AZ, United States of America

Harry O Hempy