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Date: Fri, 07 Dec 2012 16:09:43 +0100
From: Miroslav Lachman <000.fbsd@quip.cz>
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To: CeDeROM <cederom@tlen.pl>
Subject: Re: UFS2 and Journaling in 9.1-RC3
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Cc: freebsd-current@freebsd.org, Ivan Voras <ivoras@freebsd.org>
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CeDeROM wrote:
> On Fri, Dec 7, 2012 at 2:41 PM, Ivan Voras<ivoras@freebsd.org>  wrote:
>> It looks like you are confusing GEOM journalling (-J) and UFS-SU
>> journalling (-j). They are very different, and today you probably want
>> to use the latter. If you are installing 9.x from scratch, it will be
>> enabled by default. If not, you can use newfs -j or tunefs -j to enable it.
>
> "When any other means fail, read the manual" heh :-)
>
> I am still a bit confused, even after reading [1], because there is no
> explanation of difference between GJournal and SU / SU+J (which was
> introduced in FreeBSD 9.0). I understand GJournal works below
> filesystem level and I dont need to use fsck. SU/SU+J is part of the
> UDF/UDF2 filesystem. I should not use SU and GJournal at the same
> time. What are the advantages of SU/US+J? What is the advantage of
> SU+J over SU? Should I use Gjournal or SU/SU+J? Any hints welcome! :-)
>
> If I have already created UFS2 with -J, I understand I can switch it
> off, can I then simply turn of UFS+J (-j) with no data loss on
> existing filesystem?
>
> Which solution is better for drives>1TB when I dont want to wait an
> hour for fsck?

In short - if you choose Gjournal with data and journal on the same 
disk, you will have about half write speed.

If you choose SU+J, you will not be able to use UFS snapshot feature at 
this time (there is some bug and snapshots on SU+J is disabled)

Other than that - SU+J is easier to Enable / Disable on existing 
partition but is not well testet - it is younger technology than Gjournal.

Miroslav Lachman