PDS and PDSEs size grows when no new data is added.

Products

• Disk Backup and Restore - MVS
• DISK BACKUP AND RESTORE- ADD-ON OPTIO
• DISK BACKUP AND RESTORE

Issue/Introduction

Simply updating existing members will cause PDS and PDSEs to grow.

Resolution

The size of the backup/archive is based on the number of tracks allocated, not the actual amount of data written to the archive.
This can affect PDS and PDSE data sets in the following ways.

For PDS data sets, when a member is replaced the space it had occupied isnot freed and thus the PDS can grow very large even though the actual amount of data in it remains essentially unchanged.

A PDSE isn't subject to this exact problem because space for deleted members is resused, unlike PDS data sets. However, it has a similar problem in that when replacing a member the space isn't freed until the new member is actually STOWed in the data set. Therefore, if the data set is allocated with exactly the right amount of space for the members it contains, replacing a member can cause the data set to allocate more space to contain the new data but will then be able to reuse the old member's space. However, the data set will have grown and will indicate in the backup/archive report that it's larger due to the increase in allocated space.