Maintaining read performance for multiple area data sets

If you use multiple copies of your area data sets (ADSs), place the first ADS registered in the RECON data set on your fastest DASD for the best read performance.

Subsequent copies of the ADS can reside on slower DASD without affecting overall read performance.

IMS always attempts to read from the first ADS shown in the RECON list. If the first ADS is not available or if it is in a long busy state, IMS attempts to read from each subsequent ADS in the list until an available ADS is found. If all of the ADSs are in a long busy state, IMS uses the first ADS in the list.