Re: Lost file-system story

[Simon Burge <simonb%NetBSD.org@localhost>]

David Holland wrote:

> There is at least one known structural problem where atime/mtime
> updates do not get applied to buffers (but are instead saved up
> internally) so they don't get written out by the syncer.
> 
> We believe this is what causes those unmount-time writes, or at least
> many of them.

I understand the delayed atime writes were to added to reduce the number
of times a laptop harddisk spins up.  I've often wondered if a simple
sysctl could be added to control this.

Unmounting my /home on my main machine takes approximately a minute.  My
ups-nut script does

        sync
        ( cd /home; umount /home )
        sync

as soon as it gets an on-battery event so that hopefully the actual
shutdown if needed happens quickly.

Cheers,
Simon.