Subject: Re: Finding lost components in a raid set?
To: Greg Oster <>
From: Johan Ihren <>
List: current-users
Date: 02/07/2002 22:28:21
Greg Oster <> writes:

Hi Greg,

> > Basically it seems that everything has worked very nicely and I'm
> > really pleased.

Unfortunately I spoke too soon. 

My re-construction of the "failed" component with a "raidctl -R
/dev/wd2g raid1" just finished and raidctl -s now reports happiness.

But the disklabel for raid1 is zeroed.

How can that happen? I had two components out of three intact at all
times for a 2+1 RAID5 device and I see no reason to lose the label.

I have to admit that I did *not* keep a copy of that label in a safe
place, which in retrospect seems rather stupid. But I regarded the
underlying device as "safe", in the sense that an event that manage to
wipe out the label would wipe out the file system data also.

I also have to admit that I am less happy than 30 minutes ago ;-(

Losing the disklabel after what should be considered a standard
replacement of a failed component is not encouraging. But I really
don't see where I did anything wrong.


> > But, since I have no indication whatsoever that the disks should have
> > failed in any way, I cannot help being a bit curious about *both* raid
> > sets losing a component on the *same* disk without the disk being bad.
> I don't suppose you have a copy of the disklabel for that disk, do
> you?  The autoconfig should have picked it up wd2a if it had a
> disklabel type of FS_RAID (unless the component label got
> corrupted).  'raidctl -c' should have found a valid component label
> for wd2g -- the fact that it's marked as failed indicates that it
> likely didn't.

I have the label for wd2 (attached), I don't have the label for raid1,
as I said above.

> > I assume that the autoconfigured raid devices keep their configs in
> > the component labels 
> The configuration info is in the component labels, yes.
> > or thereabouts and I don't understand how both of
> > them can have been trashed at the same time. 
> I don't get that either... Was wd2 on the controller card that
> failed?  Maybe it managed to zero the component labels on you??
> Seems unlikely, but that's the only explanation I can think of so
> far...

Yes, wd2 was on the controller that failed.

> > And if the on-disk
> > configs were "bad", why didn't a "raidctl -c" fix that, if the media
> > is ok?
> "raidctl -c" uses the component labels to verify that you have the
> components listed in the right order... If a component label is
> missing (or badly out-of-sync with the remaining components), then
> that component will be marked as failed.  If you managed to get
> components in the wrong order, the RAID set shouldn't even
> configure.  (It tries quite hard to make sure you don't mess up the
> ordering, but it needs valid component labels in order to do
> that. :) )

I assume that this "component label" is stored adjacent to the device
it describes. I.e. the component label for /dev/wd2g is located at the
head of that physical partition?

Here's the disklabel for wd2. It is definitely intact, since it is
exactly the same as for wd0 and wd1:

bash# disklabel wd0
# /dev/rwd0d:
type: ESDI
disk: WDC WD1000BB-00C
label: fictitious
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 16
sectors/cylinder: 1008
cylinders: 16383
total sectors: 195371568
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0 

8 partitions:
#        size    offset     fstype  [fsize bsize cpg/sgs]
 a:    524288        63       RAID                      # (Cyl.    0*- 520*)
 b:    524288    524351       swap                      # (Cyl.  520*- 1040*)
 c: 195371505        63     unused      0     0         # (Cyl.    0*- 193820)
 d: 195371568         0     unused      0     0         # (Cyl.    0 - 193820)
 e:   8388608   1048639       RAID                      # (Cyl. 1040*- 9362*)
 f:    524288   9437247       RAID                      # (Cyl. 9362*- 9882*)
 g: 100000000   9961535       RAID                      # (Cyl. 9882*- 109088*)
 h:  85410033 109961535       RAID                      # (Cyl. 109088*- 193820)