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CA Disk™ Backup and Restore - 12.5
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FDS Capacity

Last update October 20, 2017

This page contains information about FDS Capacity including the following:

Estimating Capacity Requirements

There are two requirements for estimating FDS capacity. The first requirement is estimating the number of records the FDS should contain (FILEDEFN Specifications). The second requirement is to understand how much space (Physical space) should be allocated on the device based on the first requirement.

Maximum Capacity

Assuming that the FDS is 100 percent DSNINDEX, the maximum capacity on a 3390-9 is 3.4 GB. That equates to:

  • 14.2 million records
  • 65,536 tracks
  • 4,369 cylinders

Depending on what other subfiles are formatted in the FDS, the actual capacity will be much less.

Note: For the FDS and all its utilities to work properly, the recommended maximum capacity should be kept between 9 and 10 million records.

Estimating Subfile Capacity Requirements

Since the DSNINDEX subfile contains an entry for every data set backed up or archived, a beginning estimate is simply the number of data sets that are to be backed up with CA Disk. If CA Disk is to be used to back up all of your packs, you need to answer three questions:

1. What is the total number of data sets on these packs?

2. How many versions of each data set do you want to keep?

  • Non-SMS and/or SMS
  • Archives and/or Backups

3. How will the estimates comply with the Index Maintenance policies that manage what remains and/or are deleted from the FDS?

Estimating Physical Space Requirements

Total number of tracks = (Subfile Capacity Requirements)

                               (Records per Track)

Performance Considerations

The FDS EXCP interface is designed to optimize performance at the logical block level. Normally, higher capacity requirements utilize larger blocksizes yet the EXCP interface is designed to access these blocks in a single I/O, without performance penalty.If your DSNINDEX subfile capacity requirement is substantially less than the maximum capacity requirement for the device type and you are experiencing a high number of block splits and/or performance degradation, use the maximum capacity requirement for the device.

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