Subject: Re: soft updates Re: Summer of code ideas
To: Dieter <firstname.lastname@example.org>
From: Andrew Doran <email@example.com>
Date: 04/07/2007 12:11:51
>> > > Then for the real test start over and do it all again, but this time
>> > > after "systat bufcache" shows that most of available RAM is used up
>> > > for metadata an file data, pull the power plugs. Then try to clean
>> > > up the mess.
>> > What mess? My understanding is that with soft updates, the only
>> > thing that can possibly happen is that disk space can be lost.
>> > The background fsck is for reclaiming this lost space.
>> That's both the idea and the promise. For better or worse, that has
>> been the experience of a number of users.
> Did these users have their disk's write caches set to write-through
> mode rather than write-back mode?
For one yes, and have in the past seen pretty bad lossage when using softdep.
> NetBSD doesn't do this by default, you have to add code to /etc/rc.local.
If we get a journalling implementation that's something it can take care
of, whether it's PATA (flush the cache) or SCSI, where it can force access
to the disc.