Browse Prior Art Database

Data Movement From Reserved Areas On Direct-Access Storage Device

IP.com Disclosure Number: IPCOM000102187D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 105K

Publishing Venue

IBM

Related People

Lawrence, KJ: AUTHOR [+5]

Abstract

A new disk configuration may require some areas of the current disk configuration to become reserved. A method which requires no interaction from an end user for moving data from specified areas of a disk is disclosed.

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

Data Movement From Reserved Areas On Direct-Access Storage Device

       A new disk configuration may require some areas of the
current disk configuration to become reserved.  A method which
requires no interaction from an end user for moving data from
specified areas of a disk is disclosed.

      The environment where the data movement can take place is
restrictive.  This section describes the environment which may have
to exist for the successful completion of data movement.
 1.  The new disk configuration reserved areas must be known.
 2.  The amount and location of available space, where the data can
be moved, must be known.
 3.  The data to be moved must not be resident in main memory or in
use by any task running on the system.
 4.  Any directory which maps the disk address of the data moved has
to be updated or rebuilt.

      The new disk configuration reserved areas must be known.  Once
these areas are known, their total size can be calculated.

      The amount and location of available space, where the data can
be moved, must be known.  The amount of available space on the system
is compared to the total size of the data to be moved.  If there is
not enough space on the system to move the data from the reserved
areas, the configuration change will have to be rejected.

      The data to be moved must not be resident in main memory or in
use by any task running on the system.  This is necessary to maintain
system integrity.  When a system keeps track of the disk address of a
resident memory page, the page can get paged back out to disk without
having to do a directory lookup.  This causes problems if the data
has been moved and no longer resides at the same disk address it did
when it was paged in.  Paging it out after it has been moved could
cause duplicate data or new data which now resides there to get
over-written.  This may cause data integrity problems and/or changes
to the data to be lost.

      If there is an attempt to update a resident memory page's disk
address with its new disk location, another problem will be
introduced which complicates the design: Any resident data pages in
memory which are being moved must be frozen (not allowed to page back
out) until the move is complete and all appropriate directories
updated.

      To avoid the above problem and simplify the design, the
environment which moves the data must guarantee that the data being
moved is not resident in main memory.  This can be accomplished by
moving the data early in the IPL before the data is allowed to be
referenced; therefore, it is not resident in memory.

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