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Browse Prior Art Database

Adaptive Buffer Ratio

IP.com Disclosure Number: IPCOM000117012D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Inoue, K: AUTHOR [+4]

Abstract

Disclosed is an Adaptive Buffer Ratio which maximizes SCSI bus utilization for HDD (Hard Disk Drives). This method is easy to implement only by software without any additional hardware.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 90% of the total text.

Adaptive Buffer Ratio

      Disclosed is an Adaptive Buffer Ratio which maximizes SCSI bus
utilization for HDD (Hard Disk Drives).  This method is easy to
implement only by software without any additional hardware.

      SCSI HDD has a parameter to maximize bus
utilization/throughput.  This parameter is named "Buffer Ratio".
This parameter gives host transfer starting point to absorb
difference of transfer speed between host and drive.  When this
parameter is set properly, occurence of drive-catch-up and
host-catch-up is minimized and maximum bus utilization/throughput can
be obtained.  The notch page in mode select command can set different
Buffer Ratio values for each zone, but this page is optional.  So,
the HDD which does not support this page has only one Buffer Ratio
value across zones.  This parameter can be set by user.  If the user
sets "0" value, the HDD sets the Buffer Ratio to a fixed value.

      This Adaptive Buffer Ratio is to automatically set this Buffer
Ratio to proper values according to accessing LBA.  Buffer Ratio is
mapped proportinally between Lower Limit and Upper Limit.  Lower
Limit and Upper Limit are defined according to most inner and most
outer drive transfer speed.  The calculation is shown below.
  Buffer Ratio = Lower Limit + ( Upper Limit - Lower Limit ) *
                  LBA / Max LBA
  for example,
  when LBA = 0 , Buffer Ratio = Lower Limit
  when LBA = Max LBA / 2 , Buffer Ratio = (Lower Lim...