sttest needs to be adjusted to not run out of disk space

After eliminating some NullPointerExceptions for 10.5.1.1 (which I noticed with 10.5.1.0 testing but had also been present with 10.4.2.0) the sttest runs out of disk space before all threads are done.
Before, with the NPEs, the test would run its course in a day or two.
The test should be adjusted, with perhaps more deletes, so that it will no longer run out of disk space.