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Re: 2 Linux boxes, failover, & 1 EXT3 RAID unit

On Thu, Mar 28, 2002 at 11:16:17AM -0500, Bill Antoniadis wrote:
> Questions:
> ----------
> What will I encounter should the primary (i.e. box currently mounting /dev/sdb1)
> crash, and the backup take over?

Exactly the same as if the box crashed and rebooted.

> From my simulations, I see the backup mount
> /dev/sdb1 but I get the following in it's /var/log/messages:
> nas2 kernel: kjournald starting.  Commit interval 5 seconds
> nas2 kernel: EXT3-fs warning: mounting fs with errors, running e2fsck is recommended

Check your logs to see where the errors are coming from --- a fs with
errors needs to be checked to clear those errors.

> My limited understanding is that since both the primary box (named "nas1") and
> the secondary (named "nas2") are keeping a metadata-only journal, that data
> updates were flushed to disk (on nas1) and the metadata changes were not
> committed, thus nas2 sees an inconsistent filesystem when mounting.  Am I 
> correct?

No.  Metadata changes are being journaled, so they will be completely
consistent in the absense of disk errors.  However, you DO seem to be
getting disk errors, so you need to find out why.

> If we run with nas2 box for a while, and then decide to switch back to nas1, 
> how will nas1 and it's journal playback, react to the changes committed by nas2
> since the crash?

Well, assuming you unmount the fs from nas2 first (!), nas1 won't need
to do any journal replay at all: nas2 will have committed everything
to primary storage and the journal will be empty.


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