Understanding your current storage use and determining the unprotected/ protected storage and disk device requirements should not be taken lightly during checksum planning.
If checksumming is in your future, pay particular attention to the Unprotected Storage Per Unit Allocation. The minimal amount of unprotected storage per unit that can be allocated is five megabytes. Under-estimating this value will cause temporary objects to overflow into the protected storage area. If this condition occurs on your system, CPF message "CPI0955 - System ASP Unprotected Storage Limit Exceeded" will be issued to your system operator console every hour.
The temporary solution is to IPL your system. All unprotected objects will be deleted and the overflow condition will be reset.
You could also add additional disk capacity without having to reconfigure checksumming, but this isn't the real answer.
The permanent solution is to change your checksum configuration and allow for a larger amount of unprotected storage per unit. It is better to over- allocate the unprotected storage per unit allocation. When you get your system up and running, you can re-evaluate your allocation and dynamically reduce it. By reducing the over-allocated amount specified, you will be freeing up additional disk space to be used for data storage. This solution requires that you save and reload the entire operating system. In the future, when you add disk devices to your system, the new devices will get the amount of allocated unprotected storage that is specified in your existing checksum allocation. It is much less painful to over-allocate and reduce the unprotected storage per unit allocation than it is to increase it.
Installations with large disk configurations and slow tape drives will find themselves spending their weekend doing what should have been done on day one. Proper planning is essential to the successful implementation of checksumming. Save yourself a lot of aggravation. Do It Right The First Time!
Edward J. Koziol Kenosha, Wisconsin