How to enable Archivelog Compression and how much storage space you can save

The TSM Archive log contains all the committed transactions of TSM DB and they are later moved to the TSM DB after the successful full DB backup. If you enable deduplication and replication techniques in your environment, it is possible that your archivelog size might frequently gets to 90%. Because of this condition, you need to schedule frequent full TSM DB backups to empty the archivelog directory. 

However, scheduling frequent TSM DB backups is not practically possible in medium or large sized TSM servers. The only way is to cancel the background server processes which are generating large transactions into the active log and archivelog for some time and then resume the processes again after successful full DB backup completion.

To ease this kind of situations, from Tivoli Storage Manager Version 7.1.1, you can enable compression of the archive log files that are written to the archive log directory. You can both enable or disable compression of archive logs on the Tivoli Storage Manager server at any time. By compressing the archive logs, you reduce the amount of space that is required for storage. You also reduce the frequency with which you must run a full database backup to clear the archive log.

How to enable compression for the Archive logs

Before you configure compression of archive logs, you must also consider the pros and cons of this feature. Since every TSM server has different hardware and software settings, the results that you achieve might differ, depending on the size of the archive log files. As per IBM testing results, If you enable archive log compression, you can get 57% of Archive log storage space reduction on Linux servers and whereas you can achieve 62%  of storage savings on windows servers.

Also you must be careful if you enable the ARCHLOGCOMPRESS server option on systems with sustained high volume usage and heavy workloads. Enabling this option in this system environment can cause delays in archiving log files from the active log file system to the archive log file system. This delay can cause the active log file system to run out of space. Be sure to monitor the available space in the active log file system after archive log compression is enabled.

If at anytime, the active log directory file system usage nears out of space conditions, the ARCHLOGCOMPRESS server option must be disabled by using the SETOPT command to immediately without halting the server.

You can enable archive log compress offline and online

To enable compression of the archive log files when the server is offline, include the ARCHLOGCOMPRESS server option in the dsmserv.opt file and restart the server. The ARCHLOGCOMPRESS server option specifies whether log files that are written to the archive directory for logs are compressed.
How to enable Archivelog Compression and how much storage space you can save
You can also enable archive log compression when the server is up and up and running by issuing the SETOPT  ARCHLOGCOMPress command as YES.

You can verify that compression is enabled by issuing the QUERY OPTION ARCHLOGCOMPRESS command.

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