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Browse Prior Art Database

Dynamic Buffer Allocation for Data Transfer Requests

IP.com Disclosure Number: IPCOM000037617D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Batra, SP: AUTHOR [+5]

Abstract

This method improves performance of the Storage Subsystem by reducing the number of lost DASD revolutions.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 57% of the total text.

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Dynamic Buffer Allocation for Data Transfer Requests

This method improves performance of the Storage Subsystem by reducing the number of lost DASD revolutions.

For DASD read operations, previous implementations used a technique whereby the Storage Subsystem would transfer up to 4096 bytes of data from DASD and then suspend the Device Functonal Controller Interface (DFCI) data transfer until all 4096 bytes had been transferred to the host system. If there was more data to be transferred from the DASD, then the subsystem would set its memory addresses for both the DFCI and system-side transfers back to the beginning of the 4096-byte buffer and restart the suspended DFCI data transfer. In this way, one 4K buffer could be used repeatedly until all data had been transferred from the DASD to the host system.

Because the rate at which data transfers from the subsystem to the host is roughly one-half to one-third as fast as the transfer rate from the DASD to the subsystem, the DFCI-side transfer was often suspended for several hundreds of microseconds while it waited for the buffer to be emptied via the system-side transfer. Although the DASD devices themselves also have speed- matching buffers in the 1K to 4K byte range, it was often observed that the device buffer filled up with data read from the disk before the DFCI transfer could be restarted, causing the DASD device to stop reading from the disk. Of course, the disk itself continued to rotate and so the opportunity...