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Re: ordered data mode?



Nigel Metheringham wrote:
> 
> root hunley homeip net said:
> > Now on boot, I see:
> 
> >   mounted /dev/hda1 on /
> >   EXT3-fs: mounted filesystem with ordered data mode
> 
> > and the exact same thing for /dev/hda3 and /dev/hdb1. they all come up
> > and appear to be working. so is this normal? Or did I manage to screw
> > up somewhere?
> 
> Thats fine.
> 
> Further explanation (slightly simplified - if Stephen feels strongly
> about it I'm sure he'll give the more accurate expanded version :-) ) :-
> 
> The EXT3-fs message is just telling you it mounted the fs OK.  Its also
> telling you what form of journalling you are using.
> 
> ext3 has 2 formats of journal:-
>   - version 1 - default and only possibility for ext3 releases 0.0.3*
> and
>     earlier
> 
>   - version 2 - default for filesystems created with 0.0.4 and later
> 
> Version 2 journals support additional semantics required to allow
> metadata journalling, and provide 2 new forms of journalling - ordered
> and writeback.  Both V1 & V2 journals support data journalling (where
> everything that would go to disk is journalled).
> 
> The CHANGES file in the distribution says this:-
> 
>  New mount options:
> 
>     "mount -o journal=update"
>         Mounts a filesystem with a Version 1 journal, upgrading the
>         journal dynamically to Version 2.
> 
>     "mount -o data=journal"
>         Journals all data and metadata, so data is written twice.  This
>         is the mode which all prior versions of ext3 used.
> 
>     "mount -o data=ordered"
>         Only journals metadata changes, but data updates are flushed to
>         disk before any transactions commit.  Data writes are not atomic
>         but this mode still guarantees that after a crash, files will
>         never contain stale data blocks from old files.
> 
>     "mount -o data=writeback"
>         Only journals metadata changes, and data updates are entirely
>         left to the normal "sync" process.  After a crash, files will
>         may contain stale data blocks from old files: this mode is
>         exactly equivalent to running ext2 with a very fast fsck on
>         reboot.
> 
>  Ordered and Writeback data modes require a Version 2 journal: if you do
>  not update the journal format then only the Journaled data will be
>  allowed.
> 
>  The default data mode is Journaled for a V1 journal, and Ordered for
> V2.
> 

ahh.. now it's coming together for me. thanks. guess I'll go pore over
the code and such now and see if it makes any more sense to me..
--
Douglas J. Hunley (Linux User #174778)
http://hunley.homeip.net/

Errors have been made. Others will be blamed.





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