z/OS V1R9.0 TSO/E Command Reference

ALLOCATE CommandTo get a secondary space quantity, you need to specify SPACE(12,1)AVGREC(M). This specification provides 12 mega units of primary space and 1mega unit of secondary space. The unit of space is determined by eitherBLOCK, BLKSIZE, or AVBLOCK.If AVGREC(K), AVBLOCK(128), and SPACE(5,2) are specified, the averagerecord length is 128, the primary quantity of records is 5K, and the secondquantity of records is 2K.BLKSIZE(blocksize)specifies the block size for the data set. The maximum allowable decimal valuefor block size recorded in the DCB is 32,760.With DASD, labeled tape or spooled data set, or a TSO terminal, if you do notspecify BLKSIZE, the system determines the optimum block size for the newdata set unless you have undefined length records. For more information seez/OS DFSMS Using Data Sets.The DCB block size is determined in one of the following ways:v If USING is specified, from the attribute list. You cannot use the BLKSIZEoperand on ALLOCATE for the block size.v If you specify BLKSIZE on ALLOCATE, from the BLKSIZE operand.v If LIKE is specified and BLKSIZE is not specified on ALLOCATE, from themodel data set.With SMS, BLKSIZE is not copied from the model data set. Without SMS,BLKSIZE is copied from the model data set.v If neither USING, BLKSIZE, nor LIKE is specified, from the BLOCK operand.|The block size that you specify to be recorded in the data control block (DCB)must be consistent with the requirements of the RECFM operand:v RECFM(F) – the block size must be equal to the logical record length.v RECFM(F,B) – the block size must be an integral multiple of the logicalrecord length.v RECFM(V) – the block size must be equal to or greater than the largestblock in the data set. (Note: For unblocked variable-length records, the sizeof the largest block must allow space for the four-byte block descriptor wordin addition to the largest logical record length. The logical record length mustallow space for a four-byte record descriptor word.)v RECFM(V,B) – the block size must be equal to or greater than the largestblock in the data set. For block variable-length records, the size of the largestblock must allow space for the four-byte block descriptor word in addition tothe sum of the logical record lengths that will go into the block. Each logicalrecord length must allow space for a four-byte record descriptor word.Because the number of logical records can vary, you must estimate theoptimum block size and the average number of records for each block basedon your knowledge of the application that requires the I/O.v RECFM(U) – for files allocated to the TSO/E terminal with RECFM(U) andBLKSIZE(80), one character is truncated from the line. That character (thelast byte) is reserved for an attribute character.Specify BLKSIZE with the ALLOCATE command when using the LIKEoperand, because optimal BLKSIZE is not determined by the system for aRECFM(U) data set.Chapter 1. TSO/E commands and subcommands 29