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Self Optimizing Buffer Ratios

IP.com Disclosure Number: IPCOM000111046D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Gramann, PA: AUTHOR [+2]

Abstract

Formulas for computing a Small Computer System Interface (SCSI) Optimal Buffer Ratio in real time are disclosed. These formulas account for varying negotiated transfer periods, bus widths, zoned disk data rates, format efficiencies, and sector sizes.

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Self Optimizing Buffer Ratios

      Formulas for computing a Small Computer System Interface (SCSI)
Optimal Buffer Ratio in real time are disclosed.  These formulas
account for varying negotiated transfer periods, bus widths, zoned
disk data rates, format efficiencies, and sector sizes.

This optimal ratio is derived from the following equation.

  RO = 256 x (RS-RD) / RS
where RO is the Optimal Ratio, RS is the SCSI transfer Rate, and RD
is the effective disk transfer Rate.  The components of the formula
are computed as follows.

  RS = W / PS
where W is the negotiated bus width in bytes and PS is the negotiated
transfer period.

  RD = RR x EF
where RR is the raw disk data rate and EF is the format efficiency in
the current recording zone.  Finally, the format efficiency is
derived by the equation:

  EF = NB / (NB + OB)
where NB is the number of data bytes in a sector and OB is the number
of non-data bytes in a sector in the current recording zone.