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).
Input 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 |