Why does tracelog.exe generate a big and somewhat empty log file?

[Sygnosys]

Hi,
I'm using the tracelog command to do a trace session. After a while
running I has created a somewhat respetable file in size. The strange
thing is that if I open it with an Hex Editor it's mostly filled with
(0xFFFF). So for example for a 19Mb file if I choose to compress using
NTFS compression mecanist it will occupies on disk only 2/4Mb.
The same thing occurs with the DDK tool traceview.exe.

So my question is, why is does it generate with all this unused space?
Can it be "fixed" by some sort of configuration? (I'm not specifing
any special switch in
tracelog file configuration).


Thanks
Cláudio Albuquerque