Quite simple:

Level zeros take forever; we do them while the machine is up.

We then take the machine down to single-user and do level ones.  The number
of files which have changed since the level zero is usually much smaller,
so the dump takes less time. 

The tradeoff is in the potential time of the restoral -- if you catch
a file which was in transition, you get it from the level 1; otherwise
the level 0 suffices.

Curt Sampson sez:
/*
 * > We take an interesting approach:  We'll do a level zero while the system is
 * > up, then take it down to single-user mode a day later and do a level one.
 * > Sorry if it's not what you're looking for.
 * 
 * I don't really understand the purpose of this.
 * 
 * cjs
 * --
 * Curt Sampson  <cjs@portal.ca>  604-257-9400    De gustibus, aut bene aut nihil.
 * Any opinions expressed are mine and mine alone.
 * The most widely ported operating system in the world: http://www.netbsd.org
 * 
 */





				--*greywolf;
--
The only thing more traumatic than bootstrapping a compiler is bootstrapping
a debugger.
	-- from the notebooks of another heretic.