Browse Prior Art Database

Adaptive Background Erase Strategy for Magneto Optic Media

IP.com Disclosure Number: IPCOM000112220D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 152K

Publishing Venue

IBM

Related People

Dewey, DW: AUTHOR

Abstract

File system designed for use on magneto optic media provide the ability to preerase space so that data may be written with a two pass write (a write pass followed by a verify pass) instead of a three pass write (an erase pass followed by write and verify pass). This erasure is done at disk intialization and during background time. It is desirable to have the system transparently detect background time and perform the erasure. This disclosure covers a method to perform this background erasure. It is based on a background process polling at varying length periods and performing partial erasure. A method of selecting the areas to be erased is included.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 35% of the total text.

Adaptive Background Erase Strategy for Magneto Optic Media

      File system designed for use on magneto optic media provide the
ability to preerase space so that data may be written with a two pass
write (a write pass followed by a verify pass) instead of a three
pass write (an erase pass followed by write and verify pass).  This
erasure is done at disk intialization and during background time.  It
is desirable to have the system transparently detect background time
and perform the erasure.  This disclosure covers a method to perform
this background erasure.  It is based on a background process polling
at varying length periods and performing partial erasure.  A method
of selecting the areas to be erased is included.

      The technique consists of a system background process that will
periodically check to see if a user request has occurred to a mounted
volume over a period of time.  If none has, then it will perform an
erase.  The current practice is to use a fixed time length between
these checks whereas this method varies this time period.

      A system process (thread, task) puts itself to sleep (blocks)
for a time interval.  When it awakes, it detects if a user request
has occurred since it last went to sleep.  If user requests have
arrived, then the process puts itself to sleep again without
performing any erase.  If no user requests have arrived, then it will
perform erase acitivity for a set period of time known as the "system
work interval".  The period the process sleeps for is termed the
"cleanup polling period" and is a variable quantity.

      The process begins in an interactive mode and uses one
algorithm to select the cleanup polling period and extents to erase.
If no user requests have arrived for an extended period, it
eventually switches to a batch mode and uses a different method for
extent selection.

Interactive Mode Polling Period Selection:

      The initial polling period used is determined by the state of
the disk.  This volume depends on the percentage of free space that
is unerased.  The larger the percentage the larger the polling
period.  Every time it is determined that a user request has arrived
during a sleep interval, the polling period is calculated and used.
If instead the volume was found idle for the polling period and a
short period of erase activity was performed, a smaller polling
period is used.

      With this approach the background erase will not interfere with
user response but will detect background.  While using a disk the
user will not be interfered with, but once it sets idle the system
will convert to perform the necessary work.  As the percentage of
erased free space declines the background process will attempt more
activity since the initial polling period will be less.

An exact embodiment is the following:

Let there be 3 constants defined by the user or system:

TMAX = Maximum amount of initial polling period

TMIN = Minimum amount of initial p...