Browse Prior Art Database

Adaptive Positioning of Streaming Tape Drive

IP.com Disclosure Number: IPCOM000041961D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Lockett, DE: AUTHOR

Abstract

In streaming operation, a tape drive depends upon continuous tape motion at its regular velocity for high efficiency performance. In a typical operation, the host system commands the drive to read a given record, and after the record has been read, the host supplies another command to read the next following record. If the host system does not supply the read command within a following interval defined as a reinstruct window, then the drive must stop and reposition itself for access to the next data block. This repositioning is normally called back-hitching and requires a significant time which degrades the effective overall performance of the drive. An improved technique is described which allows a drive of the streaming type to operate in either a continuous "streaming" mode or in a start/stop mode.

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Adaptive Positioning of Streaming Tape Drive

In streaming operation, a tape drive depends upon continuous tape motion at its regular velocity for high efficiency performance. In a typical operation, the host system commands the drive to read a given record, and after the record has been read, the host supplies another command to read the next following record. If the host system does not supply the read command within a following interval defined as a reinstruct window, then the drive must stop and reposition itself for access to the next data block. This repositioning is normally called back-hitching and requires a significant time which degrades the effective overall performance of the drive. An improved technique is described which allows a drive of the streaming type to operate in either a continuous "streaming" mode or in a start/stop mode. By monitoring the requirements of the host system and switching the tape drive between the continuous start/stop mode, an overall improvement in efficiency can be attained. The drive, while operating in the streaming mode, counts the number of misses which occur and require back- hitch operations. When this count reaches an arbitrary number, for example, five in a row, then the drive is switched from continuous operation to start/stop mode. In the start/stop mode, the drive is stopped automatically after each record is read and then started up again to read the next record. This is a slower individual record mode of operati...