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Re: ordered data mode?



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.


-- 
[ Nigel Metheringham           Nigel Metheringham InTechnology co uk ]
[ Phone: +44 1423 850000                         Fax +44 1423 858866 ]
[ - Comments in this message are my own and not ITO opinion/policy - ]






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