Subject: Re: "buffer cache locking" meets "soft updates"
To: Ethan Solomita <>
From: Thor Lancelot Simon <>
List: tech-kern
Date: 10/27/1999 04:37:48
On Wed, Oct 27, 1999 at 12:32:41AM -0700, Ethan Solomita wrote:
> 	I've been trying to come up to speed with Soft Updates. The company I
> work for is looking to use NetBSD, and we're hoping to be able to use
> Soft Updates with it. If you don't know about it, the quicky summary:
> Kirk McKusick is adding some sophistication to ffs which will eliminate
> the need for nearly all synchronous meta-data writes, without switching
> over to a log-based filesystem.

There is a branch of the CVS repository for this, and Frank Van der Linden
is actively working on it.

Since we do, actually, have a working LFS implementation in NetBSD (which
is maintained by Konrad Schroder) there's less reason to really need
"soft updates" for most applications.  LFS has other advantages over
FFS, as well:

	* fast, safe startup with no *need* for "fsck", whether in the
	  background or foreground.
	* better data organization for many purposes (on filesystems with
	  many directories, FFS *forces* long seeks).
	* Plays nicer with RAID (because it can always write the stripe
	* Can be relatively easily extended to do snapshots, online
	  backup, and other greasy kid stuff.

If you're looking for a filesystem programming project you might consider
whether your time might be at least as well spent working on LFS.  In
particular, we could use an optimizing cleaner (I can provide references
to good papers on this topic) and snapshot support.