Browse Prior Art Database

Optimized Look-Ahead Extension on Sequential Access

IP.com Disclosure Number: IPCOM000118218D
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Kakihara, T: AUTHOR [+4]

Abstract

Disclosed is an algorithm of optimizing a look-ahead extension timing on sequential read access of a Hard Disk Drive (HDD). The practical data transfer rate of the host system is traced. When the read head reaches the start sector for the look-ahead extension, the remaining data amount in the cache memory is compared to the estimated transferred data amount for the next one revolution. Go/no-go decision of the look ahead extension for the revolution is determined with the results of the comparison.

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Optimized Look-Ahead Extension on Sequential Access

      Disclosed is an algorithm of optimizing a look-ahead extension
timing on sequential read access of a Hard Disk Drive (HDD).  The
practical data transfer rate of the host system is traced.  When the
read head reaches the start sector for the look-ahead extension, the
remaining data amount in the cache memory is compared to the
estimated transferred data amount for the next one revolution.
Go/no-go decision of the look ahead extension for the revolution is
determined with the results of the comparison.

      While only sequential read access is issued, the look ahead
should be always extended for further prefetch.  However, on actual
access, it is not a rare case that the sequential access is suddenly
stopped and the previous data which has already been accessed is
requested again (read back).

      The local MPU on the HDD starts a local timer on a read command
receiving (Fig. (1)).  If the consecutive read is sequential access,
MPU memorizes the elapsed time as a required time for N blocks data
transfer (Fig. (2)).  While sequential read access is issued, MPU
repeats the measurement and updates the required time for N*2, N*3
blocks (Fig. (3,4)).....  Meanwhile, MPU traces the head position on
the current  track.  When the read head approaches the start sector
for the look-ahead  extension, the remaining data amount in the cache
memory, which the host  will request after that, is compared to th...