> But our power is down every 1~2 week.

Ouch.  A UPS will help, but even with a UPS you can get a hang/crash
that corrupts data.  So a UPS is for riding through short outages,
it is NOT a guarantee that the machine never goes down hard.

> Once power down occurs, the NetBSD server will check file system
> at next startup, it will take as long as 10 minutes.

What you want is:

	FFS
	soft updates
	disk's write cache turned off
	background fsck

This works great on FreeBSD.  No lost data.  No corrupted data.
Machine is available immediately after boot.  (Note that the
background fsck does use up some resources, such as disk i/o.)

Does NetBSD 4.0 have background fsck?

> I have done a test on Linux (ext3), it take only 10 seconds to recover.

But Linux's ext will CORRUPT YOUR DATA!!!  (I'll give you one guess how
I know this.)  Who cares how fast it boots if your data is corrupted?

> So, I think ffs v1 is not suitable for my environment.

FFS is fine.  Linux ext is crap that corrupts data.