In message <200408021146.14474.junyoung@mogua.com>, Bang Jun-Young writes:
>Hi,
>
>Is there a disk wipe out utility for NetBSD, a program that fills
>unused blocks of the file system with 0 without destroying data?
>It's mostly used for security but I need it for backup purpose
>so the entire image of the NetBSD partition is compressed in less
>size.
>
I haven't seen one, but it would be very easy to write a simple one -- 
create a file, and go into a loop writing a zero byte every 512 bytes.  
In fact, if you want to go through the file system instead of writing 
to the raw disk it's hard to see how to make it any better.

What are you using for backup?  Dump(8) doesn't dump the free blocks, 
so their value doesn't matter.

		--Steve Bellovin, http://www.research.att.com/~smb