Plan for journal use of auxiliary storage

If you are journaling an object, journal management writes a copy of every object change to the journal receiver. It writes additional entries for object level activity, such as opening and closing the object, adding a member, or changing an object attribute. If you have a busy system and journal many objects, your journal receivers can quickly become very large.

The maximum size for a single journal receiver varies. It depends on how the system allocates the journal receiver across multiple disk arms. The maximum size ranges from approximately 1.9 GB to 1.0 TB depending on what value you specified for the associated journal's receiver size option.

To avoid possible problems with a journal receiver exceeding the maximum size allowed on the system, specify a threshold for the receiver of no more than 900 000 000 KB if you specified a journal receiver maximum-size option for the associated journal. Otherwise, specify a threshold of no more than 1 441 000 KB.

The following topics provide more information about how journal management affects auxiliary storage:

• Functions that increase the journal receiver size
• Methods to estimate the size of a journal receiver
• Journal receiver calculator
• Methods to reduce the storage that journal receivers use
• Determine the type of disk pool in which to place journal receivers
• Journals and independent disk pools

• Frequently asked questions about journaling and disk arm usage
  Journaling affects the disk arms that store the journal receiver.
• Functions that increase the journal receiver size
  Some optional functions available with journal management can significantly increase auxiliary storage requirements.
• Methods to estimate the size of a journal receiver
  You can use the methods below to estimate the effect a journal receiver will have on auxiliary storage.
• Journal receiver calculator
  Use the journal receiver calculator to estimate the size of your journal receiver.
• Estimate the size of the journal receiver manually
  Use this procedure to estimate the size of your journal receiver.
• Methods to reduce the storage that journal receivers use
  Reduce the size of journal entries by methods such as journaling after-images only, or specifying certain journaling options including the Fixed Length Data (FIXLENDTA) option on the Create Journal (CRTJRN) and Change Journal (CHGJRN) commands.
• Determine the type of disk pool in which to place journal receivers
  Use disk pools (auxiliary storage pool) to control which objects are allocated to which groups of disk units. If you are journaling many active objects to the same journal, the journal receiver can become a performance bottleneck. One way to minimize the performance impact of journaling is to put the journal receiver in a separate disk pool. This also provides additional protection because your objects are on different disk units from the journal receiver, which contains a copy of changes to the objects.
• Journal management and independent disk pools
  Independent disk pools are disk pools 33 through 255. Independent disk pools can be user-defined file system (UDFS) independent disk pools or library-capable independent disk pools.