Allocating direct output lines
You can specify record format, logical record length, and block size when you allocate direct output lines.
For direct SYSOUT lines defined to IMS, you can use any valid output device supported by the operating system's BSAM. You can specify the following record formats: F, FM, FB, FBM, FBS, FBSM, V, VM, VB, and VBM. You can specify block sizes, but these are adjusted downward at execution time if they are larger than system-definition maximums.
For fixed-format records, the system-defined buffer size must be at least 20 bytes longer than the DCB block size for the data set. For variable-length records, the buffer size must be 16 bytes longer than the desired block size, including Block Descriptor Word and Record Descriptor Word. To accommodate the data to be written, you can select logical record specifications that are restricted as follows:
- For fixed-format records, the block size must be an even multiple of logical record length.
- For unblocked variable-format records, maximum logical record length equals block size minus 4, and must include the RDW (4 bytes).
Table 1 lists device types and the corresponding default data set values for direct output data sets. If you do not supply DCB parameters, these default record format, logical record length, and block size values apply.
| Device Type | RECFM | LRECL | BLKSIZE |
|---|---|---|---|
| 3211 | VM | 137 | 141 |
| 2540P | V | 84 | 88 (note 1) |
| 2400 series tape | VBM | 125 | (note 2) |
| DASD | VBM | 125 | 1/4 Track |
- Control characters are not supported.
- Block size only depends on system-definition buffer size. Each
segment is treated as a logical record. When you specify blocking,
all segments of a message are contained within a block, unless the
block size is not large enough.
Fixed-length segments are padded with trailing blanks. If blocking is used, the balance of the block is also padded when a message does not have the same number of segments as logical records in the block.
Tape blocks are not shorter than 18 bytes, regardless of the record format.
Because volume switching is provided by operator command when tape is used, specify a large value (for example, 99) for the volume count subparameter of the VOLUME keyword on the associated DD statement. In an IMS system in which binary synchronous devices are also operating, and only one tape drive is allocated, timeout problems can occur.