Browse Prior Art Database

Fast Second Migrate of Data from On-Line to Removable Media

IP.com Disclosure Number: IPCOM000105466D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Anglin, MJ: AUTHOR [+4]

Abstract

Hierarchy Storage Management (DFHSM) balances the overall system performance/cost by migrating less active data to a slower and less expensive device such as a tape drive. Automatic recall is used to bring the data back when needed. DASD is the common device for on-line storage and tape is an example of removable media. Because the data maybe changed, and because only one copy of the data is kept in the hierarchy, the tape data image is not kept after the recall. Each migration is treated as an independent event, regardless of previous tape data image. Multiple migrations create many copies of the data on tape. All the old copies will be deleted and the latest copy retained. This processing of tapes, which is unnecessary if the data is not changed, is addressed by this disclosure.

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

Fast Second Migrate of Data from On-Line to Removable Media

      Hierarchy Storage Management (DFHSM) balances the overall
system performance/cost by migrating less active data to a slower and
less expensive device such as a tape drive.  Automatic recall is used
to bring the data back when needed.  DASD is the common device for
on-line storage and tape is an example of removable media.  Because
the data maybe changed, and because only one copy of the data is kept
in the hierarchy, the tape data image is not kept after the recall.
Each migration is treated as an independent event, regardless of
previous tape data image.  Multiple migrations create many copies of
the data on tape.  All the old copies will be deleted and the latest
copy retained.  This processing of tapes, which is unnecessary if the
data is not changed, is addressed by this disclosure.  The system
described below will retain the initial copy and not make an
identical duplicate copy.

      If a recalled file has not been changed, there is an
opportunity to do a second migrate without involving any tape mount
or tape write process.  This is a significant performance improvement
for applications where the data is never altered.  In order to bring
about this function, a file system has to detect when the file data
has been altered.  Other file attributes, such as authorization, can
be changed without impeding this function.  If the content of a file
(the part stored on tape) was changed after it was recalled, the fast
second migrate is not applicable.

      The main advantage of this system is the speed of second
migration for read/only data and the savings in tape mount and tape
write.

      Invalid files on tapes can only be removed by recycling the
tape, which is an expensive process.  By minimizing duplicate copies,
this design also reduces the work needed to recycle tapes.

      The first migration of data creates a very compact and
organized group of tapes.  With the old method, the locality of
reference of the data will be destroyed by read references.  This
disclosure will keep the...