I came to much the same conclusion - assuming it was bootvis, but I can't be sure - from reading things here and there it seems to me that it would start this trace.log to find out what's going on with the system so it could optimize it, and then it should shut it off when it was finished with it - the problem was, it never got shut off and thus, the never ending file.... It's just a theory, I've got lots of 'em wanna hear the one about the fast food and the diet industry???