Keeping a certain number of Backup generations.

Products

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

Issue/Introduction

How to keep a certain number of Backup generations?

Resolution

For non-SMS data sets you can limit the number of Backup + Archive generations using IXMAINT parameter COPIES=n. 
However, this will still be the maximum number of generations as expired entries are deleted by IXMAINT anyway. 

Similar considerations apply also for SMS data sets. 

The following 2 SMS MC attributes define the maximum number of Backup versions: 
- Number of Backup Versions Data set Exists on Primary (MC). 
- Number of Backup Versions Data set Deleted from Primary (MC). 

Also, you can limit the number of Backup + Archive generations for SMS data sets using IXMAINT parameter COPIES=n,SMSNOSMS 

However, this is again the maximum number of generations as expired entries are deleted by IXMAINT due to following 2 SMS MC attributes: 
- Retain Days Only Backup Version Data set Deleted (MC). 
- Retain Days Extra Backup Versions (MC) 

Refer Disk tech doc for "SMS and IXMAINT" for details on these SMS attributes. 

So in summary, you can define a maximum number of Backup/Archive generations, for example 3, but you cannot guarantee or retain 3 generations. 

If an entry is expired, it is deleted anyway.