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Channel Data Transfer Rate Queued by a Rate of Channel Data Overrun

IP.com Disclosure Number: IPCOM000059700D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Disbrow, JR: AUTHOR [+2]

Abstract

This invention relates to a hierarchically managed staged storage system in which the data transfer (data rate) capacity of concurrent accessing paths exceeds that of the host system, resulting in a variable length queue of buffered records. More particularly, the invention relates to a method of minimizing queue lengths by an intermediate staging level varying the path's transfer rates inversely with queue length. In the prior art, bandwidth allocation among bulk storage devices attaching a common directed loop by assigning cycles as a function of their transfer rate is shown, for example, in [1]. However, in hierarchically managed staged storage systems, such reallocation of cycles may be rendered more difficult. Illustratively, the staged storage system to which this invention pertains may be found in [2].

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Channel Data Transfer Rate Queued by a Rate of Channel Data Overrun

This invention relates to a hierarchically managed staged storage system in which the data transfer (data rate) capacity of concurrent accessing paths exceeds that of the host system, resulting in a variable length queue of buffered records. More particularly, the invention relates to a method of minimizing queue lengths by an intermediate staging level varying the path's transfer rates inversely with queue length. In the prior art, bandwidth allocation among bulk storage devices attaching a common directed loop by assigning cycles as a function of their transfer rate is shown, for example, in [1]. However, in hierarchically managed staged storage systems, such reallocation of cycles may be rendered more difficult. Illustratively, the staged storage system to which this invention pertains may be found in [2]. Such a system includes multiple CPUs or their channel proxies accessing shared DASD (direct access storage device) strings by way of multiple paths mediated by storage control units (SCUs). During high I/O activity, the SCUs may not be able to respond in time to a request for a storage cycle from a channel, particularly in the case of low priority channels. This devolved because the SCU can only handle a maximum data transfer rate that is less than the sum of allowable maximum data rates at all possible connected channels. This delayed response from the storage control unit may cause channel data overrun to be detected by that portion of the storage control unit performing data transfer with a channel. Performance can be improved if the SCU can tune the speed of the channel data transfer according to the rate of channel data overrun. During the time of high overrun r...