Browse Prior Art Database

Offset Retry Method for Paralleled Track DASD

IP.com Disclosure Number: IPCOM000109778D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 2 page(s) / 83K

Publishing Venue

IBM

Related People

Burton, PT: AUTHOR [+4]

Abstract

Disclosed is a solution to the problem of reading interleaved data of paralleled track direct access storage device (DASD) when it has been written by more than one data head, each with a different offset in relative radial position not only with respect to the servo head, but also with respect to the other data heads.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Offset Retry Method for Paralleled Track DASD

       Disclosed is a solution to the problem of reading
interleaved data of paralleled track direct access storage device
(DASD) when it has been written by more than one data head, each with
a different offset in relative radial position not only with respect
to the servo head, but also with respect to the other data heads.

      As data is read, the device computes subblock check, block
check and cyclic redundancy check (CRC) syndromes to determine the
data's integrity.  If noncorrectable data is detected, a number of
retries at reading the data are performed.  If the read still fails,
the device assumes that the data was written by a data head offset
from the servo head.  The device initiates an offset retry sequence,
performing reads at incrementally greater offsets from the servo
track center until high integrity data is read.

      A paralleled track DASD reads data simultaneously from two or
more tracks, typically on the same actuator.  But each data head on
the actuator may have a different offset with respect to the servo
head.  Thus the offset retry function described above for
single-track reading must be modified to read multiple tracks.

      The solution is the proposed method for reading paralleled
track DASD such that the results of two or more sequential reads
under different offset conditions can be combined in a way that
provides full error correction and detection capability.  The
described sequence applies to two-track reads, but can be adapted for
reading multiple tracks.
      1.   Offset A is established.
      2.   The data record is read.  The detected data from heads 0
and 1 is interleaved as in a normal read and transmitted to the
attachment buffer.  However, the data and check bytes from head 1
which are input to the syndrome generation are all forced to '00'X.
The head 1 data transmitted to the attachment can be actual data as
read or forced to zero.
      3.   All subblock check, block check and CRC syndromes...