by Robert Sample » Wed Mar 31, 2010 5:04 pm
There is a requirement that every data set in the catalog be unique. However, if a sequential data set is not cataloged, there can be any number of copies of it on disk or tape. Keeping track of where they are, however, becomes a challenge since they can only be found by looking at the actual volume. Most sites discourage the use of uncataloged data sets due to problems in locating them.