See http://www.nabble.com/derbyall-test-uses-%7E11Gb-disk-space-when-run%21-t530808.html#a1433024 :
"I discovered that when I now run the derbyall test it uses ~11Gb disk space!
I find 4 x 10 "..../multi/Tester*.out" files which each is ~270Mb! (=>
I will upload a patch which makes ij/mtTester.java able to tell if the mtTester detected errors, which then is used by harness/MultiTest.java to decide if the .out file can be deleted.
mtTester is currently only used by harness/MultiTest.java.