vinum revive does not rebuild parity (was vinum rebuildparity, when?)

Stijn Hoop stijn at win.tue.nl
Tue Sep 7 21:52:29 PDT 2004


On Wed, Sep 08, 2004 at 11:28:46AM +0930, Greg 'groggy' Lehey wrote:
> >> [...] the parity surely is not correctly recalculated during
> >> the revive.
> 
> If that were the case, the parity would be incorrect at offset 0.
> Yes, it is recalculated.

Of course -- I hadn't thought of that.

> >> Greg, can you tell me if this is correct behaviour?
> 
> Sorry for the slow response.  I was at a conference last week.  No,
> it's not correct.

No problem; this is still a volunteer project last time I checked.
In a way I am glad to hear that it is not correct.

> > While not having heard back yet, I had to rebuild another subdisk,
> > but I decided to do it off-line this time. Turns out the parity was
> > rebuilt ok. 
> 
> Yes, this is what I recommended.

OK.

> > Might there be a bug in the online rebuild code?
> 
> Looks like it.
> 
> The current version of Vinum is on its last legs.  Lukas Ertl is
> rewriting it, so don't expect much change in this version.  For the
> time being, just accept that you should umount before rebuilding a
> plex.

I will; it's just that somehow I was led to believe that I didn't need
to do that. This has caused me some pain in the past.

May I suggest applying the attached patch to /usr/src/sbin/vinum/vinum.8?
At least it would prevent someone else from making the same mistakes as
me.

Thanks for your response,

--Stijn

-- 
The problem is that there are several people in design positions now who
couldn't design the Next Big Thing(TM) unless it involved them taking a
photocopier and someone else's design of The Next Big Thing(TM).
		-- 'Alkaiser' in a post on Slashdot on game originality
-------------- next part --------------
--- vinum.8.orig	Wed Sep  8 06:47:46 2004
+++ vinum.8	Wed Sep  8 06:51:19 2004
@@ -441,6 +441,10 @@
 .Ic checkparity
 prints a running progress report.
 .Pp
+It is advisable to always check the parity of a RAID-4 or RAID-5 plex after
+an unclean shutdown. Corrupt parity is as bad as degraded mode for such a
+plex; if one of the subdisks of such a plex fails, data corruption will occur.
+.Pp
 .It Xo
 .Ic concat
 .Op Fl f
@@ -1046,6 +1050,11 @@
 flag is specified,
 .Ic rebuildparity
 prints a running progress report.
+.Pp
+At present, a bug prevents rebuildparity from correctly completing its job
+when the vinum volume is mounted and being accessed. You should only rebuild
+the parity of plexes on unmounted volumes in order to guarantee correct parity
+checks.
 .Pp
 .It Xo
 .Ic rename
-------------- next part --------------
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