Journaling affects the disk arms that store the journal receiver.
How the journal receiver affects the disk arm depend on several factors:
The following are frequently asked questions about journaling and disk arm usage:
How many arms in my disk unit will journaling use?
Which journal parameters and settings affect the number of the disk arms the journal receiver uses?
Why is the system not using the new disk arms I added to my disk pool?
How many disk arms the journal receiver uses depends on your threshold value and whether you use a maximum receiver-size option. When you create a journal receiver and attach it to a journal that does not specify a maximum receiver-size option, the system spreads the journal receiver on up to 10 disk arms. If you use a maximum receiver-size option, the system spreads the journal receiver on up to 100 disk arms. Some rules that the system uses when determining the number of disk arms are as follows:
You can use the following formula to determine how many disk arms you will use:
Number of disk arms = Journal receiving threshold setting / 64 MB
For more information about disk arm use and journaling see Striving for Optimal Journal Performance on DB2® Universal Database for iSeries™.
The threshold for the journal receiver and whether you use a maximum receiver-size option have the largest effect on how many disk arms the journal receiver uses. If you have a system which is before V5R2, removing internal entries also affects the number of disk arms that are used.
There can be a several reasons. First, to use the newly added disk arms, you must perform a change journal operation to attach a new journal receiver. Also, the system does not necessarily use all of the disk arms in a disk pool. If you are not using a maximum receiver-size option, the most disk arms the system will spread the receiver over is ten. The number of disk arms the receiver uses also depends on the threshold you use for your journal receiver. If you use a maximum receiver-size option and increase your threshold, it is more likely that your new disk arm will be used.
If you use system-managed access-path protection (SMAPP), the system generates internal journal entries to protect the access paths for database files. If you have not upgraded to at least V5R2, setting your journal receiver to remove internal entries is an issue if you are not producing these internal entries. Before V5R2, removing internal entries can steal disk arms from the normal journal entries. For example, if you have six disk arms in the disk pool housing your journal receiver and remove internal entries, two arms are dedicated to the internal entries and four arms are used for your regular journal entries. If you do not produce any internal entries, those two arms remained idle. For V5R2 and later, this is not an issue.
For more information about disk arm use and journaling see Striving for Optimal Journal Performance on DB2 Universal Database for iSeries.
The journal receivers probably use some disk arms more than other because of the way journal management writes journal entries to disk. When the system produces journal entries, journal management stores the journal entries in memory. When it is ready, journal management sends the journal entries to a disk arm in one group. When the next group of journal entries are ready, journal management sends the entries to the next disk arm. Journal management continues in this sequential manner until all of the disk arms it uses have received a group of journal entries. The cycle then repeats.
You can spread out the usage by increasing your threshold and using a maximum receiver-size option.
For more information about disk arm use and journaling see Striving for Optimal Journal Performance on DB2 Universal Database for iSeries.