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Improved Tape Integrity Checking During Restore Operation

IP.com Disclosure Number: IPCOM000122210D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 86K

Publishing Venue

IBM

Related People

Frank, MM: AUTHOR [+3]

Abstract

Described is a method of verifying that data blocks read from magnetic tape media contain the data expected. Data blocks are made "self-defining" so that each block read from media can be checked to ensure it contains the expected data before the data is used.

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

Improved Tape Integrity Checking During Restore Operation

      Described is a method of verifying that data blocks read
from magnetic tape media contain the data expected.  Data blocks are
made "self-defining" so that each block read from media can be
checked to ensure it contains the expected data before the data is
used.

      Fig. 1 shows a typical method of storing data on magnetic tape.
Data is stored on the tape in the form of data blocks.  Each data
block contains a logically contiguous set of bytes which can be
transferred to and from the tape media via a single read or write
operation. Multiple data blocks may be grouped together to form a
tape file, and a tape file may be completely contained within a
single tape volume or may span multiple volumes.  Data is only valid
within the context of a single tape file;  data from multiple tape
files cannot be intermixed.

      Data blocks are made "self-defining" by generating a unique
identifier for each block to be written, concatenating the block
identifier to the user data for the block, and writing the resulting
concatenation to the tape media as a single tape block, as shown in
Fig. 2.  The block identifier is created by generating a unique file
identifier (such as a timestamp) when it is determined that the next
block to be written starts a new tape file, and combining this file
identifier with the relative sequence number of the block within the
tape file to form the complete block identifier.

      When reading the data blocks back from tape, the block
identifiers are used to verify that the correct blocks are being read
by comparing the expected file and sequence identifiers against the
identifiers read.  As new files are encountered on the tape, the
expected file and sequence identifiers are reset using the values
read from the first block in the file.  A difference between the
expected and actual value of an identifier results...