IBM E16RMLL-I Implementation Guide - Page 228
Defining the database backup trigger
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Note: If you are changing the recovery log to rollforward mode, the recovery log size must be increased. To estimate the new value, reset the cumulative log consumption statistic using the administrative command reset logconsumption. Monitor the cumulative consumption over a number of days. Divide the cumulative consumption by the number of days since you reset the value, to get an average value. A safe size for the log pool is around 30-40% larger than this figure. 5.4 Defining the database backup trigger The database backup trigger determines when to back up the Tivoli Storage Manager database, based on the recovery log utilization. When the recovery log is in rollforward mode, the potential for it to fill up is much greater than in normal mode. If the recovery log fills up, it is possible that the server can stall or even halt unexpectedly. By defining a database backup trigger, when the recovery log usage reaches the defined percentage, the server database is automatically backed up. The backup operation clears the cached transactions, clearing the recovery log. Use the define dbbackuptrigger command to define settings for the database backup trigger, such as the percentage of the assigned capacity and device class to be used for automatic database backups. You can also define the number of incremental database backups that can be run before a full backup must run. These settings are used only when the recovery log mode is ROLLFORWARD. The actual percentage to choose depends on the planning considerations discussed in Chapter 2, "Implementation planning" on page 15. We recommend using 75% as a starting point and use the default number of incrementals (six). Monitor your environment's activity to make sure that you do not trigger database backups too frequently, as this creates unnecessary load on the server and increases tape mount activity. If database backups are triggering too frequently, consider increasing the recovery log size. Example 5-7 shows how to set the limit of 75% and run up to six incremental database backups before a full database backup. Example 5-7 Setting the database backup trigger tsm: LOCHNESS_SERVER1>def dbbackuptrigger devclass=lto2-dc logfullpct=75 numincremental=6 incrdevclass=lto2-dc ANR2282I Database backup trigger defined and enabled. tsm: LOCHNESS_SERVER1>query process 198 IBM Tivoli Storage Manager Implementation Guide
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