On Thu, 25 Mar 1999, Mason Loring Bliss wrote:

> On Thu, Mar 25, 1999 at 12:30:51PM -0500, Jim Wise wrote:
> 
> > _The Designn and Implementation of the 4.4BSD Operating System_, by
> > McKusick et al has a section describing LFS.  It's not very long, but it
> > gives a good overview/introduction.
> 
> Hm... Things are busy at work, so I haven't yet looked at the online
> references folks have sent, but I do happen to have my copy of the 4.4BSD
> book with me. (I'm reading it through straight, and hadn't reached the bit
> about LFS yet.)

It's in Chapter 8, Local Filestores, in section 8.3, "The Log-Structured
Filesystem".

> >From my reading, it actually seems that LFS is *less* stable in some ways
> than FFS, not more... My interest in soft updates / JFS is the stability
> you see when, for instance, your power is dropping during the middle of a
> write. LFS doesn't seem to really be aiming at the same thing as JFS or
> soft updates. I don't see it as being something I can point to as being
> the right thing for the place at which I'm working at the moment, whereas
> soft updates or a journalled filesystem would be a big win.

As I understand it, soft updates are an orthogonal issue.

I think LFS is aming at the same thing JFS is. In LFS, data are written in
lumps, with checksum (CRC). If the CRC on a lump fails, then the lump is
not valid. So changes either happen or they don't happen, as opposed to
FFS where you can have parts of a change happening.

I think LFS has that same loose-power stability of JFS, though JFS might
have the exact process refined.

Take care,

Bill