Browse Prior Art Database

Adaptive Skew Optimization

IP.com Disclosure Number: IPCOM000116738D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 80K

Publishing Venue

IBM

Related People

Hashimoto, M: AUTHOR [+4]

Abstract

Disclosed is an Adaptive Skew Optimazation which maximize Hard Disk Drive (HDD) performance. Each skew is calibrated by Format command according to characteristic of each HDD.

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This is the abbreviated version, containing approximately 53% of the total text.

Adaptive Skew Optimization

      Disclosed is an Adaptive Skew Optimazation which maximize Hard
Disk Drive (HDD) performance.  Each skew is calibrated by Format
command according to characteristic of each HDD.

      The HDD has access to data on disk by sector.  The sectors are
located in tracks on disks.  The HDD has access to continuous sectors
across the tracks by switching the head and/or seeking 1 tracks.  For
the head-switching or seeking, it takes time to be ready to
read/write
the next track.  If the start sector of the next track is located at
the
same position from the index of tracks, it always misses one
revolution
and waits until the start sector comes under the head.  The following
shows the simple example.
    Assumption : 10 sectors per track
             Read from sector 7 to 12 (12 sectors)
             Head switching time is 2 sector time
      CASE 1
             Index
             V
    Track 0      9    0    1    2    3    4    5    6    7    8
    Track 1     19   10   11   12   13   14   15   16   17   18

Flow of Read Operation
  1.  wait sector 7
  2.  sector 7 comes under the head
  3.  start reading from sector 7
  4.  read sector 8 and 9
  5.  switch head to track 1
  6.  head becomes ready (It takes 2 sector time as head switching
       time)
  7.  sector 12 is under the head, wait sector 10 (worth to 8 sector
       time)
  8.  sector 10 comes under the head
  9.  start reading sector 10
 10.  read sector 11 and 12

      To Minimize the waiting time like above in 8., the start sector
of the next track is shifted by some sectors.  This is called "Skew".
The read operation is as follows.
      CASE 2
             Index
             V
    Track 0      9    0    1    2    3    4    5    6    7    8
    Track 1     17   18   19   10   11   12   13   14   15   16

Flow of Read Operation
  1.  wait sector 7
  2.  sector 7 comes under the head
  3.  start reading from sector 7
  4.  read sector 8 and 9
  5.  switch head to track 1
  6.  head becomes ready
  7.  sector 10 is under the head
  8.  does not need...