multiple MTD partitions

[Artem Bityutskiy]

Joel Stanley wrote:
> It makes a hello of a lot of sense in the scenario you describe.
> 
> However, how will this positive effect be negated by data loss due to
> loss of power? There will be times where power is unexpectedly
> removed, and I would expect this scenario to be common with our user
> base.
> 
> JFFS2 has done an excellent job, at least on my xos, of keeping
> filesystem integrity after sudden power-offs.

Joel,

Ivan and Bernardo have already made very good explanation on this. Yes, if you 
mount UBIFS with -o sync flag, you'll end up with the synchronous FS, just like 
JFFS2. Or your applications have to open files with O_SYNC, or coll functions 
like fsync().

Yes, JFFS2 is very good in recovery, and this comes very naturally from its 
simple design.

In UIFS we have whole subsystem which is responsible for recovery after unclean 
reboots (fs/ubis/recovery.c). To recover, UBIFS has to replay the journal and 
remove all the garbage from the flash media. The garbage are the half-written 
UBIFS nodes in the journal (very similar to JFFS2 nodes). While JFFS2 leaves 
garbage on the media and prints CRC error messages on every reboot, UBIFS 
cleans it up during recovery procedure.

Design-wise, I may also add that UBIFS journal is like a small JFFS2 inside 
UBIFS. From time to time the journal is committed, which means the indexing 
data structures are updated. The commit process is atomic. And the commit does 
not involve double copying of the journal data, the data physically sits at the 
same place, but gets indexed, and UBIFS picks other logical eraseblocks for the 
next journal.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)