JCL allocation of work data sets

The amount of required work space is dependent on many factors such as virtual storage and type of devices used, but is especially sensitive to the file size of the input data set.

Because of the number of variables involved, an exact formula cannot be given for calculating the needed work space. However, the following guidelines usually hold true:

For fixed length record (FLR) sort applications, 1.5 to 2 times the input file size is usually adequate.
For variable-length record (VLR) sort applications, 1.5 to 2.5 times the input file size is usually adequate.

These guidelines assume that a reasonable amount of storage (at least 1M) is available to DFSORT. Limiting the available amount of storage can increase the amount of needed work space.

DFSORT can often run with less than the amount of work space indicated by the guidelines described previously in this section.

To get the best performance using JCL allocation of work data sets:

Use devices without much activity on them.
Use high-speed disk devices such as IBM's TotalStorage DS8000 subsystems for work data sets, and avoid using tape or virtual (VIO) for work data sets.
Allocate space in cylinders.
Specify contiguous space for each work data set, and make sure there is enough primary space so that secondary space is not needed.
Allocate two or more work data sets.
Use multiple channel paths to the devices.
Use different volumes and separate channel paths for the work data sets and the input/output data sets.

The following table shows the work data set space needed with 4M of storage for applications with various characteristics when Hipersorting, dataspace sorting, and memory object sorting are not used (HIPRMAX=0, DSPSIZE=0 and MOSIZE=0).

Table 1. Work Space Requirements for Various Input Characteristics
Work Space Requirements for Various Input CharacteristicsInput Data set Characteristics				Cylinders (3390)
Filesize (MB)	FLR/VLR	Max LRECL	BLKSIZE	Input Data Set	Work Data Set
4	FLR	80	27920	6	6
4	FLR	160	27840	6	6
20	FLR	80	27920	26	36
20	FLR	160	27840	26	36
20	FLR	1000	27000	26	36
40	FLR	80	27920	51	56
40	FLR	160	27840	51	56
40	FLR	1000	27000	52	56
150	FLR	160	27840	189	198
4	VLR	300	27998	6	9
40	VLR	300	27998	51	63
40	VLR	6000	27998	55	59
150	VLR	300	27998	188	200
150	VLR	6000	27998	203	200