mode data=journal in ext3. Is it safe to use?

[Phil White]

Petter,

I was never able to resolve the problems I had with data=journal with the
2.4 kernel.  I did *not* try the 2.6 kernel though, so I can't give you
any data points there.  In the end, I settled for data=ordered, and have
never seen the problems I described in my original posts.  Also, to give
you some background, I had been using ReiserFS before switching to ext3,
and I experienced a lot of corruption with Reiser (my company makes linux
based appliances which sometimes get turned off while under heavy IO). 
Since ReiserFS doesn't do data journalling (metadata only), we
consistently ended up with corrupt files.  After this, I decided to try
ext3 with data=journal, and I never even got far enough with load testing
to try the 'hard reset' test.  It would consistently crash in the fs code
under heavy load.

We have since had no problems with data=ordered, and since it writes data
blocks before writing metadata to the journal, we don't see corrupt files
anymore (even on hard resets).

If data integrity (within the file) is important to you in the face of a
crash or power loss, do NOT use ReiserFS or ext3 data=writeback.   If your
application never overwrites data in files, you will be just fine using
data=ordered (appending to files or creating new files is pretty much
guaranteed to never cause corruption).  If you need to overwrite data in
files, you need to use data=journal (and probably beg people to fix it) or
rewrite your application to use some other method (i.e. copy the file,
delete the old one) and just use data=ordered.

--Phil

>
>
> Petter Larsen wrote:
>
>>
>> Data integrity is much more important for us than speed.
>>
>
>
> You might want to consider ReiserFS or one of the others which were
> designed with journaling in mind.  And I hope you're using RAID1 or RAID5.
>
>