OSAM buffer sizes

For OSAM data sets, choose a buffer size that is the same as a valid block size so that buffer space is not wasted. Valid block sizes for OSAM data sets are any size from 18 to 32768 bytes.

Note:

If you plan to use IMS utilities such as DFSUDMP0, you must specify a block size of less than 32768. DFSUDMP0 adds a 15 byte prefix to each image copy output record which cannot exceed 32767.

The buffer sizes (in bytes) that you can choose when using OSAM as the access method are:

512
1024
2048
Any multiple of 2048 up to a maximum of 32768

Restriction: When using sequential buffering and the coupling facility for OSAM data caching, the OSAM database block size must be defined in multiples of 256 bytes (decimal). Failure to define the block size accordingly can result in ABENDS0DB from the coupling facility. This condition exists even if the IMS system is accessing the database in read-only mode.