vinum rebuildparity, when?

[Stijn Hoop]

Hi,

thanks for your response, I didn't notice it at first because it only
went to the mailing list :)

On Wed, Aug 25, 2004 at 12:08:53PM +0200, Christian Laursen wrote:
> Stijn Hoop <stijn at win.tue.nl> writes:
> > I was wondering about the vinum 'rebuildparity' command, especially the
> > times when one needs to use this.
> 
> I run rebuildparity if checkparity finds any errors after unclean shutdowns.

OK, that's what was adviced.

> > The problem is that I can't find anything in the vinum docs about this
> > command other than it's purpose. What I don't understand is the difference
> > between reviving a disk in a RAID-5 plex, and rebuilding the parity.
> 
> When reviving a disk the data on that disk is calculated from the data and the
> parity on the other disks.

Yes, but the parity should be recalculated at the same time, right?

> I think rebuildparity only reads data and writes the parity calculated
> from that but for all disks.

OK, that would seem logical.

> > When I start a degraded disk it starts to revive -- which led me to believe
> > that vinum was also recalculating the parity. Evidently it wasn't.
> > I'm therefore now updating my procedures to always run
> > 'checkparity -v <plex>' after a disk crash.
> 
> That shouldn't be neccesary.

Well, it appears to be. checkparity found some errors in the parity after
a single disk crash & rebuild (ie degraded mode -> start subdisk -> revive
process complete).

If this is not the expected behaviour it means something about the controller
has blown; we do get lots of unexpected read/write errors which always turn
out to be false alarms upon further inspection. Maybe a controller has
turned bad :(

FWIW, the rebuildparity helped, the parity is now again correct.

--Stijn

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