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Re: EXT3 on raid with external journal...



Kurt, was there any consensus on this thread?
I am running tests on the same configuration (ext3 on
RAID, with external journal)- are there any particular
tests that you had run? I could run it on my systems
too and post the results in the mailing list.



--- Kurt Fitzner <kfitzner excelcia org> wrote:
> Matt Bernstein wrote:
> > On Apr 13 Kurt Fitzner wrote:
> > 
> > There could be metadata which is only in the
> journal, so failure probably 
> > means reboot + full fsck, so you may as well use
> ext2 if your machine 
> > doesn't otherwise crash.
> > 
> > Far preferable, I think, would be to put your
> journal on a RAID 1 pair.
> 
> I would like to think that if the ext3 driver
> encountered an error 
> writing to the journal, that it would then skip the
> journal and write 
> straight to the device - reverting to ext2 behavior.
>  There should never 
> be any loss of data (meta or otherwise) upon the
> failure of a journal 
> device.  That is, unless the failure of the
> journaling device coincides 
> with a power failure.  That is:
> 
> 1) Failure of journaling device
> 2) Attempted write of metadata to journal device
> 3) Power failure before ext3 gives up on the
> journaling device
> 
> In that scenario, the ramification is the array
> requiring a full fsck. 
> The benefit of running the journal on an external
> device would far 
> outweigh the cost of a full fsck in the unlikely
> event the above happens.
> 
> I need to know, though, what exactly is the behavior
> of ext3 in the 
> following situations:
>   - At system startup if there is a failure to
> "mount" an external journal
>   - During operation if the external journal device
> fails.
> 
> Does ext3 then revert to non-journaled (ext2)
> behavior in those instances?
> 
>   -
> 
> 
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