Ext3 users - Mar 2002 - 2 Linux boxes, failover, & 1 EXT3 RAID unit

Hello,

Setup:
------
I have two RedHat 7.2 (2.4.9-31) boxes that are attached to one external RAID
unit.  Both boxes are able to see the RAID unit as /dev/sdb1, but only
one box mounts (cat /proc/mounts yields: /dev/sdb1 /nas ext3 rw 0 0) the unit
at any give time.  The other box listens, via heartbeat (linux-ha), waiting to
mount the RAID unit, should it''s sibling crash (actually, heartbeat no
longer
heard via serial and ethernet).  The /nas directory is NFS exported with the
rw,sync,no_wdelay options to several Linux and Tru64 boxes.

Questions:
----------
What will I encounter should the primary (i.e. box currently mounting /dev/sdb1)
crash, and the backup take over?  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
nas2 kernel: EXT3 FS 2.4-0.9.11, 3 Oct 2001 on sd(8,17), internal journal
nas2 kernel: EXT3-fs: recovery complete.
nas2 kernel: EXT3-fs mounted filesystem with ordered data mode.

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?

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?

Would it be safer to always run e2fsck on nas2 takeover, prior to mounting
/dev/sdb1?

Am I wrong in choosing EXT3 over EXT2 in this setup?

Any help is greatly appreciated.

Thanks in advance,
Bill Antoniadis

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.

--Stephen