| If you are considering using spiralog for your Rdb database files,
please strongly consider the attached paper from Oracle Rdb
Engineering. And, btw, you would move files to a spiralog volume just
the same as you would move them to any other volume (in Rdb's case,
probably via RMU/RESTORE or perhaps RMU/MOVE). It also sounds like
you ought to read the spiralog documentation set; it will answer most
of your questions.
norm lastovica / oracle rdb engineering / colorado springs
[Oracle Rdb] Oracle Rdb and Spiralog
Copyright (c) Oracle Corporation 1996. All rights reserved.
SOURCE: Oracle Corporation, Oracle Rdb Engineering
WHAT IS SPIRALOG?
The Spiralog File System for OpenVMS Alpha is a new file system from
Digital Equipment Corporation that co-exists with the current OpenVMS file
system (called Files-11 or ODS-2). Spiralog co-exists with the existing
OpenVMS file system, allowing existing applications to run unchanged.
Spiralog is a log-structured file system where all data (both user data and
file system metadata) is stored in a log. Whereas update-in-place file
systems write data to specific disk locations, Spiralog writes all data to
the tail of the log. The data written may make earlier parts of the log
obsolete. The new data is called live data; the obsolete data is called
stale data. A part of Spiralog called the cleaner reclaims the disk space
used by stale data, such as files that have been deleted and parts of files
that have been updated.
Those interested should contact Digital Equipment Corporation for
additional information about Spiralog. Information on Spiralog may also be
found on the World Wide Web at 'http://www.openvms.digital.com'.
WHAT ABOUT ORACLE RDB AND SPIRALOG?
As when any new storage technology is being considered, customers
considering Spiralog volumes for storage of Oracle Rdb databases are
encouraged to ensure that applications work correctly by testing them,
under load, in a non-production environment before placing the application
into production using Spiralog volumes for storage of Oracle Rdb databases.
Care should be taken to test error conditions (application failures, system
failures, power failures, etc.) as well as the backup and recovery strategy
to ensure that data protection measures are at a level appropriate for the
data being processed.
Oracle Rdb engineering has performed limited testing of Oracle Rdb versions
V6.0-15, V6.1-04 and V7.0 using the Spiralog V1.0-1 File System. No Oracle
Rdb functionality problems have been observed relating to use of Spiralog.
At this time, no performance testing has been done to determine the effects
of Spiralog volumes on Oracle Rdb performance.
Customers are cautioned that they must continue to use the Oracle Rdb RMU
BACKUP command to create backup copies of Oracle Rdb databases. Like the
OpenVMS BACKUP utility, the Spiralog SAVE utility is not supported for
backing up Oracle Rdb databases. RMU BACKUP is the supported way to backup
Oracle Rdb databases.
WHAT ABOUT SPIRALOG CACHING?
A significant feature of Spiralog is the three caching options available
(write-behind caching without flush on close, write-behind caching with
flush on close, and write-through caching). Understanding the effects of
the various caching schemes is important in order to make the correct
decision about caching for your application. Very careful consideration
should be given to the level of caching to be enabled especially if either
form of write-behind caching is being evaluated for Oracle Rdb files. Note
that the files of an Oracle Rdb database include the recovery-unit journal
files, after-image journal files, data storage areas, snapshot storage
areas and the root file.
The Spiralog User's Guide (part of the Spiralog documentation set) includes
detailed information about the 3 caching options. Oracle Rdb does not
perform any of the program calls to control any caching attributes of the
file system. Any changes that need to be made to a Oracle Rdb file must be
made with the OpenVMS SET FILE command with the /CACHING qualifier to
control the caching attribute.
WHAT ABOUT USING SPIRALOG WRITE-BEHIND CACHING?
If Spiralog write-behind caching is enabled for any Oracle Rdb files and a
system failure (power failure, system crash, etc.) occurs, there is a
possibility that required Oracle Rdb file I/O operations were not complete
due to the write-behind cache not being flushed to disk before the system
failed. Since the order of I/Os that Spiralog flushes to disk is not
predictable, an Oracle Rdb database may be left in an inconsistent state in
such a situation and it may not be possible for RMU/VERIFY to detect the
inconsistencies. Because of this, Oracle recommends that you do not use
Spiralog write-behind caching for any of the following Oracle Rdb database
file types:
- After-image Journal Files (.AIJ)
- Recovery-unit Journal Files (.RUJ)
- Storage Area Files (.RDA and .SNP)
- Root Files (.RDB)
Temporary files (such as sort work files) may be safely placed on Spiralog
volumes with write-behind caching enabled.
[R] Oracle Rdb is a registered trademark of Oracle Corporation.
[R] Spiralog and OpenVMS are registered trademarks of Digital Equipment
Corporation.
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