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Selective Recombination of Free Space Data Types with a Background Task

IP.com Disclosure Number: IPCOM000108776D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 110K

Publishing Venue

IBM

Related People

Gregg, LE: AUTHOR [+2]

Abstract

For a re-writable optical disk, this article describes a method to minimize the unnecessary work of pre-erasing freed space that might later be needed, and it minimizes the synchronous wait time required because an erase must be completed before some space can be used.

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

Selective Recombination of Free Space Data Types with a Background Task

       For a re-writable optical disk, this article describes a
method to minimize the unnecessary work of pre-erasing freed space
that might later be needed, and it minimizes the synchronous wait
time required because an erase must be completed before some space
can be used.

      After data is written on a read/write optical disk, the disk
must be "erased" before new data can be written at the same location.
One problem maintaining an optical disk then becomes - when, if ever,
should an area which has been freed be erased?  This article
describes a method to minimize both the unnecessary work and the wait
time because an erase must be completed.

      Free, ready-to-write space on optical disk is maintained in a
balanced tree.  The key used to access the tree of free space is the
disk address of the space.  This technique allows rapid location of
space located "near" some other space.  If it is necessary to locate
a space of a particular size, an initial candidate is located from
searching the tree and then the links between the leaves of the tree
can be used to locate another larger free area nearby if the initial
candidate is not large enough.

      To erase space which has been written on and later made
available, a "background" task is used which simply erases space
during processor and optical disk time which is not otherwise
required.

      The technique described here expands the use of the free-space
tree to include space that is "available" for use, but it must be
erased first.  This space is referred to as "almost-free".  The data
record of the free-space tree is expanded to include a flag which
indicates if the space is free-and-erased, or just free but needing
to be erased.

      With the additional information in the free-space tree, several
additional options become possible.  F...