Data set allocation rules

When you allocate a partitioned or sequential data set and use the Data Set Characteristics page of the New Data Set wizard to specify record format, record length, and block size, the Developer for z/OS product enforces the following rules:

• With any value of record format except U, either record length or block size is required, and both can be specified. A zero value is the same as being unspecified. If you omit both record length and block size, the wizard prompts you with the message Record Length: must not be empty or Block Size: must not be empty.
• If record format is F, FA or FM and both record length and block size are specified, they must be equal. Either value defaults to the other value. If you attempt to enter differing values for record length and block size, the Developer for z/OS interface prompts you with the message For the selected record format, the values of record length and block size must be equal when both are specified.
• If record format is FB, FBA, or FBM, and both record length and block size are specified, block size must be a multiple of record length. If you specify record length without block size, OPEN calculates an optimal value for block size that depends on the device type. If you attempt to enter a value for block size that is not a multiple of record length, the Developer for z/OS interface prompts you with the message For the selected record format, the value of block size must be a multiple of record length when both are specified.
• If record format is V, VB, VA, VBA, VM, or VBM and both block size and record length are specified, block size must be at least four more than the record length value. If you specify record length without block size, OPEN calculates an optimal value for block size that depends on the device type. It is at least four more than the record length value. If you attempt to specify a value for block size that is less than four more than record length, the Developer for z/OS interface prompts you with the message For the selected record format, the value of block size must at least four more than the value of record length when both are specified.
• If record format is VA, VBA, VM, or VBM, record length must be at least 5. If you attempt to specify a value for record length that is less than 5, the Developer for z/OS interface prompts you with the message For the selected record format, the value of record length must at least 5.
• If record format is U, block size is required, and record length is disabled. If you omit block size, the wizard prompts you with the message Block Size: must not be empty.