mkfs.jffs2 propsal and a question about burst reads

[Bjorn Wesen]

On Tue, 6 Nov 2001, Jörn Engel wrote:
> > Well, you can think of a log-structured filesystem as "all journal," so the
> > "J" applies.
> 
> As far as I recall, the "trick" with journaling filesystems is to log
> only the metadata. On normal hard drives, this speeds up the most

I think the history was the other way around - the systems which log also
the data as opposed to metadata were introduced later. The literature
about journaling filesystems seems a bit vague on the subject, so I don't
see it as any problem to put all filesystems of this type in a class and
call it "journaling". After all, it's a journal with or without userdata.. 

The name "log structured" is equally confusing since your normal
journaling system is also centred around a log :)

> Real log-structured filesystems are considered slow in every-day
> useage and to my knowledge only one was ever implemented for some bsd
> flavor.

Datalogging as opposed to simply metadata logging is necessary on a flash
because you can't rewrite blocks at random. It's probably not a good
technique on a harddisk except if you really want to guarantee actual file
consistency on a crash, but that would require transactional user-mode
support anyway (something we've discussed on jffs-dev some times). 

/BW