Journaling UFS with gjournal.

[Pawel Jakub Dawidek]

On Thu, Jun 22, 2006 at 03:37:12PM +0200, Oliver Fromme wrote:
+> Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
+>  > Rong-en Fan wrote:
+>  > +> I think I must miss something in this announcement. How
+>  > +> much space will be used for journal? For example, if
+>  > +> the provider is 80G, how much I will lost due to gjournal?
+>  > 
+>  > The size of the journal don't depend on file system size. It more depend
+>  > on your disk speed and file system load. For example your disk can write
+>  > at 60MB/s. Journal switch time is 10 seconds. The journal provider has
+>  > to have place to keep two journals (active and inactive). So bascially
+>  > you need 60*10*2MB + gjournal headers. I think 2GB is a safe default.
+> 
+> But what happens in the case when you have only one provider?
+> You wrote that you can specify only one provider (e.g. one
+> partition) to gjournal, which will be used for both journal
+> and file system data.  In that case, how do you tell how much
+> space is used for the journals and how much space is left for
+> the file system?  It didn't become clear from the examples in
+> your initial mail.

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.

+> 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.

+> 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.

+> 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.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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