Frank van der Linden (frank@wins.uva.nl) has brought Kirk  McKusick's
 trickle sync + FFS soft update code into the main tree. It has had some
 moderate to heavy testing over the last month. He's currently using it
 on his /usr filesystem and the filesystem containing all his sources
 on his main NetBSDdevelopment machine, and did not have a problem since
 fixing the last known bug (2.5 weeks ago).

To use it, do the following: 

         1. Update your sources. 
         2. Compile a new kernel with "options SOFTDEP" in your kernel
            config file.
         3. Run the new kernel.
         4. Install the new include files from sys/sys (i.e. at least do
            cd /usr/src/sys ; make includes). To be safe, just install
            them all (cd /usr/src ; make includes)
         5. At least recompile libc, sbin/mount, sbin/fsck_ffs,
            sbin/tunefs, and install them.
         6. Run "tunefs -n enable /dev/rXd0x" to enable soft updates on
            the filesystem(s) of your choice.
         7. Remove "update=YES" from your /etc/rc.conf file.
            update(8) is no longer needed. Its work is now done in a 
            more sophisticated way by a kernel thread.
         8. Reboot 
         9. Have fun testing.
 
If you have any problems, please send PRs, or mail Frank, with
as much detail as you can gather.  

Note that this code is on the experimental source tree, not on the
NetBSD-1.4/1.4.1 release branch. The next formal release to use it
will be NetBSD-1.5.