Journaling UFS with gjournal.

[Oliver Fromme]

Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
 > There is no manual page for gjournal(8) yet. There is an option you can
 > use to specify journal size:
 > 
 >         # gjournal label -s 2147483648 ad0
 > 
 > This will create 2GB journal and the rest will be for the data.

Cool.  I guess you can also specify the journal switch
interval as an option, right?

Oh, by the way:  Are both UFS1 and UFS2 supported?

 > +> Another question:  What happens if you (accidentally) make
 > +> the journals provider too small, so it hits the end before
 > +> the next regular switch?
 > 
 > Currently it will panic, but I'm working on it.

OK.  Actually I already guessed that it would panic.  :-)
It probably would be better to block all write requests
and wait until the other journal has been written out, so
it can be re-used.  And print(9) a message so the admin
knows what kind of problem there is.

However, if the size of the journals provider is twice the
maximum raw transfer rate of the disk multiplied by the
switch interval time (as you recommended), it should be
impossible to get a journal overrun.

 > +> PS:  I've also sent a follow-up to the -fs mailing list a few
 > +> days ago, containing a few questions ...  did you overlook it?
 > 
 > If you haven't CCed me, I probably did.

I see.  I'm sorry for that.  I'll forward you a copy if
you don't mind.

 > +> PPS:  Thanks again for all your work on journaling!  It
 > +> looks very cool and promising.  Any plans to commit it?
 > +> A wider audience will speed up the process of polishing
 > +> the rough edges, I think.
 > 
 > There are some decisions I need to make before it will go to HEAD. Like
 > 'gjournal' mount option.

I see.  I hope there won't be problems with that.

Bringing journaling support to UFS is a significant
milestone in FreeBSD's history.

Best regards
   Oliver

-- 
Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
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