UFS2 Journaling implementation detail

[Unga]

--- Ivan Voras <ivoras at freebsd.org> wrote:

> >  Does it log anywhere if the journal size is too
> small for the system load?
> 
> Yes, you'll get a system panic in this case. Yes,
> it's a bad solution, complain to Pawel :)
> 

So the gjournal can corrupt the file system as well as
can fix it :)

I think this is a serious concern for desktop users
rather than servers. For those who do multi-channel
audio encoding, HD/35mm-full-frame video encoding,
batch conversion of photos, etc. may hit the default
1GB journal size and end up in system panic.

I think because of this gjournal implementation issue,
gjournal requires a huge journal.

Just for a thought, in my opinion, gjournal should not
use the entire journal for logging. May be split it
two. Ie. From size S given, use two journals. When one
journal is full, point the new changes to go to the
second journal, and flush the first journal and so on.
If the gjournal has to flush too often, then log it in
the system log that journal is too small. 

Ivan, thanks again for detail.

Kind regards
Unga




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