On Fri, 21 May 1999, Manuel Bouyer wrote:

> On Thu, May 20, 1999 at 09:23:45PM +0400, Oleg Polyanski wrote:
> > 	they are very different. xfs is an ordinary (but extremely optimized
> > for high speed data access) journaling file system and stores the transaction 
> > log somewhere on the disk (in other slice of disk or in the slice of another
> > disk or inside the filesystem itself). lfs is a log-structured file system,
> > there is no transaction log or data - file system itself is a log. lfs is
> > good in many terms but unfortunately it is write only file system; data
> > reading without notable performance impact is impossible. lfs is an example
> > of excellent research work but in real life it is unusable.
> 
> Hum, the few tests I ran on LFS showed it to be faster than ffs for reading
> as well. Do you have some numbers ?

Someone else in another discussion of LFS described the point I think Oleg
was refereing to. That a highly fragmented file will read very slowly on
an LFS (as the data are in multiple segments). That doesn't mean reading
is slow, just a highly-fragmented file will read slow.

Likewise FFS will WRITE slowly to such a file. So it's just a difference
in where the penalty is paid. Also, with LFS, if the cleaner runs, you
should get back a quickly-read file.

Take care,

Bil