Browse Prior Art Database

Recorded Access of Logical Data Considering Physical Data Location

IP.com Disclosure Number: IPCOM000108761D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 85K

Publishing Venue

IBM

Related People

Flannagan, WJ: AUTHOR [+2]

Abstract

Disclosed is an algorithm that takes a request to read some amount of logical data, and if it requires reading data from multiple physical locations, reorders the reading of the logical data in a manner that considers the physical location of the data.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 73% of the total text.

Recorded Access of Logical Data Considering Physical Data Location

       Disclosed is an algorithm that takes a request to read
some amount of logical data, and if it requires reading data from
multiple physical locations, reorders the reading of the logical data
in a manner that considers the physical location of the data.

      One of the normal methods of storing data on a disk is as a
related collection of data stored in a file or dataset. When data is
stored this way, there will be a description, called an extent map,
which will describe the relationship between the logical ordering of
the data (Figure 1) and its physical location on the disk (Figure 2).
The logical ordering of the data may differ from the physical
ordering of the data on the disk.

      Usually, when the dataset or file is read from the disk, only
the logical ordering of the data is considered in determining how the
data will be read into a memory buffer (Figure 4).  This approach to
reading the data can cause non-sequential disk seeks when logical
ordering and physical ordering of the data differ.

      If there were one request to read all twenty-one sectors of the
sample file or dataset, then the request would be satisfied without
regard to the physical location of the data.  If the algorithm is
applied, then the ordering of the requests would be changed, as
exemplified in Figure 3.

      The algorithm is defined as follows:  Reorder the list of
physical locations assoc...