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Browse Prior Art Database

Multiple Concurrent Use of a Streaming Tape Data Path

IP.com Disclosure Number: IPCOM000034715D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 80K

Publishing Venue

IBM

Related People

Blades, JA: AUTHOR [+4]

Abstract

A method of data buffering and physical interface management permits the concurrent use of an I/O processor data path for both low-speed (e.g., streaming tape) and high-speed (e.g., DASD) data transfer operations. In its most general form, an I/O processor (IOP) data path consists of a storage port, a device port, and one or more interposed data buffers. The storage port connects the IOP buffer to the host processor's main storage bus, and the device port connects the IOP buffer to some device interface. Idle time for the data ports are especially frequent and lengthy when the data rate of a given port is significantly higher than the average data rate of a connected I/O device.

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Multiple Concurrent Use of a Streaming Tape Data Path

A method of data buffering and physical interface management permits the concurrent use of an I/O processor data path for both low-speed (e.g., streaming tape) and high-speed (e.g., DASD) data transfer operations. In its most general form, an I/O processor (IOP) data path consists of a storage port, a device port, and one or more interposed data buffers. The storage port connects the IOP buffer to the host processor's main storage bus, and the device port connects the IOP buffer to some device interface. Idle time for the data ports are especially frequent and lengthy when the data rate of a given port is significantly higher than the average data rate of a connected I/O device. To better utilize data path resources for a multiplicity of devices, a data path management discipline can take advantage of the differences in the average data rates between the high-speed data ports and the relatively low speeds

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of typical streaming tape units. In particular, this discipline can dynamically disconnect the storage port from a data path during tape data transfers to allow other I/O operations to use that storage port at times when it is otherwise idle. A data buffer within the IOP is dedicated to the tape operation. This data buffer consists of N contiguous elements, in which the size of each element corresponds to the size of a tape data burst. The number, N, of tape buffer elements depends upon the average data rate of the tape media relative to that of the IOP storage and device ports. N is chosen such that the transfer rate of the storage port allows at least one other storage operation, as well as the transfer of at least one tape data burst, before the device port requires that burst. A tape write operation follows this sequence of events. 1. Connect the storage port to the tape buffer and

initiate the fetch of the first burst of tape data from

main storage. Until this first burst of data resides

in the tape buffer, the IOP does not recognize any

request by the tape device for the data.

2. Continue to fetch data bursts from storage until

all of the N burst buffers are full or until the

storage data is exhausted. When either condition

occurs, release the storage port from the tape and

initiate any other storage operations that are now

pending for the storage port.

3. Upon filling the first buffer from storage, the IOP

can respond to the initial data request from the tape.

When the tape data request occurs, initiate the device

port transfer of that first...