Defining online log data sets
These topics describe tasks related to defining OLDSs.
Choosing dual or single OLDS logging
IMS can log information to a single data set or to two identical data sets.
Defining the number of OLDSs
You must define at least three OLDSs (or OLDS pairs) to start IMS. However, you can define additional OLDSs (up to 100).
Defining space for each OLDS
When defining the size of each OLDS, you also need to consider the size and location (DASD or tape) of the SLDS. If the SLDS is on tape, consider the size of an SLDS volume and how often you intend to archive the OLDS.
Defining a block size for the OLDS
The main factor that determines OLDS block size is the track size of the OLDS devices. The OLDS block size cannot exceed the device track size. Define a block size that maximizes the amount of log data per track (for example, half-track for 3380 or 3390 DASD). Because IMS writes only full OLDS buffers to the OLDS, a large OLDS block size results in more efficient use of DASD space.
Defining devices for the OLDS
You configure the OLDS so that a system failure that renders an OLDS inaccessible does not stop the entire system. If you define dual OLDS logging, define each data set in an OLDS pair on different devices and, if possible, on different control units and channels.
Changing OLDS characteristics
Before you scratch and reallocate an OLDS that has been archived, you must delete the log control record in the DBRC RECON data set for this OLDS by using the
DBRC DELETE.LOG OLDS(
ddname
) SSID (
name
) command.
Defining OLDS buffers
You can define from 2 to 9999 OLDS buffers (the default is 5). The number of buffers can be changed during IMS restart.
Parent topic:
Specifying your choices for the log data sets