Number of journal buffers
- Default value
- The default for z/OS and z/VM is
NSERVS + NSUBTKS + 1. The default for z/VSE is 1, because z/VSE does not support multiple journal buffers.
- Parameter type
- Where set
Cannot be reset
In z/OS, the NJBUFF parameter can be set explicitly only via the PARM field in the EXEC card. See Specifying EXEC statement parameters.
In z/VM, the NJBUFF parameter is stacked in the EXEC that issues all the FILEDEFs.
- Related products
- Model 204 V2.1
The NJBUFF parameter has a dual role of allocating the number of channel programs and journal buffers.
NJBUFF can be 1, or
NSERVS + NSUBTKS + 1, or any value larger than
NSERVS + NSUBTKS + 1. Setting NJBUFF to a value greater than 1 invokes multiple journal buffers and ensures that a free buffer is always available for the journal.
In z/OS only, the NJBUFF setting is automatically recalculated when the setting is greater than 1 and less than or equal to
NSERVS + NSUBTKS + 1. The initial value of NJBUFF is used to define the number of channel programs (NCP) for the journal data set. Sizing NJBUFF to the value calculated in the formula guarantees the optimal number of NCP for the journal data set.
The NJBUFF parameter has the following options:
|0 or is omitted||The default value is used.|
|1||Only one buffer and one channel program (NCP) is obtained. All puts and waits are synchronized. Recommended only when NUSERS=1.|
||The specified number of buffers is obtained.
If the value is greater than 255 and 31-bit BSAM is allowed, only 255 NCPs are obtained.
If 31-bit BSAM is not allowed, only 99 NCPs are obtained.
If the buffer number is larger than the NCPs, for example,
|For z/OS only:
Greater than one and less than or equal to
|The value is recalculated by Model 204 as: |