Where to start?

[Vasil Dimov]

[discussion moved from freebsd-hackers@ to freebsd-geom@]

On Tue, Jan 23, 2007 at 09:19:59 +0100, Oliver Fromme wrote:
> Vasil Dimov wrote:
>  > Mike Silbersack wrote:
>  > > Soeren Straarup wrote:
>  > > [...]
>  > > > I'm looking for a project.
>  > > [...]
>  > > I'd like to see the ability to run gjournal without reformatting.
>  > > If you could create a dummy file inside the filesystem, then use
>  > > that area for the journal, it might be possible.  I'm sure that
>  > > would let a lot more people see if journalling is right for them.
>  > 
>  > I am not sure about gjournal internals but what if a system crash
>  > occurs in the middle of a transaction and the fs gets corrupted and
>  > the data, necessary to fix it is in the journal, but you cannot
>  > access the journal because the file, which contains the journal,
>  > is on a corrupted fs?
> 
> I think you should still be able to mount the file system
> read-only, even if it's not "clean", so there's no problem
> locating the journal file.  Particularly, note that the
> journal file should probably be located in the root of the
> file system, and it will have a constant size and should
> be allocated from the start (i.e. it never grows nor
> changes allocation), which means there is no way that its
> meta data could be damaged.
[...]

With gjournal not only the metadata is journaled but also the actual
data (e.g. files' contents). So writes to the journal file (which is a
"regular file" on the FS) should bypass the journaling stuff. Otherwise
they will get journaled themselves and it will end up in an endless
loop.

This thing still looks to me like roping your chest to your leg (instead
of to an unmovable object) in order to avoid falling, but I might be
wrong...

-- 
Vasil Dimov
gro.DSBeerF at dv
%
A complex system that works is invariably found to have
evolved from a simple system that works.
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