Re: raid10 devices all marked as spares?!

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On 05/29/12 00:07, NeilBrown wrote:
On Mon, 28 May 2012 22:50:03 +0200 Oliver Schinagl<oliver+list@xxxxxxxxxxx>

Hi list,

I'm sorry if this is the wrong place to start, but I've been quite lost
as to what is going wrong here.

No, you are in exactly the right place!
Pfew :D

I've been having some issues latly with my raid10 array. First some info.

I have three raid10 arrays on my gentoo box on 2 drives using GPT.
I was running 3.2.1 at the time but have 3.4.0 running at the moment.
mdadm - v3.2.5 - 18th May 2012

md0, a 2 far-copies, 1.2 metadata, raid10 array  consisting of /dev/sda4
and sdb4.
md1, a 2 offset-copies, 1.2 metadata, raid10 array consisting of
/dev/sda5 and sdb5
md2, a 2 offset-copies, 1.2 metadata, raid10 array consisting of
/dev/sda6 and sdb6

I'm liking the level of detail you are providing - thanks.
The more information provided, the better I always recon!

sd*1 is bios_grub data, sd*2 is 256mb fat for playing with uefi and sd*3
is 8gigs of unused space, may have some version of ubuntu on it and sd*7
for swap.

For all of this, md0 has always worked normally. it is being assembled
from initramfs where a static mdadm lives as such:
/bin/mdadm -A /dev/md0 -R -a md /dev/sda4 /dev/sdb4 || exit 1

In general I wouldn't recommend this.  Names of sd devices change when
devices are removed or added, so this is fragile.  It may cause the actual
problems you have been experiencing currently.
Yes! Yes yes yes! I know. Kinda offtopic here, but:

I've always used a small 100mb -250mb (or 1gb on my desktop) array using metadata 0.9 and autodetect. This worked perfectly. /usr, /home etc where on exotic raid setups (metadata 1.2 etc) but this all just worked (tm).

Recently Fedora decided booting and /usr was a mess and not long after udev (i belive not only in gentoo) 'agreed' that /usr and / should be merged.

With 0.90 autodetect being depreciated by the kernel anyway I decided to bite the bullit and use my 8gb /usr as combined / and /usr. Now however I was 'forced' to also use an initramfs to get my raid array going. Long story short, I just quickly hacked that together as minimally as possible, as I haven't found any 'clean' way to do it/documented/recommended way to copy.

It's not only just error-prone, It's also broken. Having a disk missing or fail, causes kernel panics due to init pre-maturly failing because mdadm fails at finding /dev/sdb.

md1 and md2 are being brought up during boot, md0 holds root, /usr etc
wheras md1 are just for home and data.

The last few weeks md1 and md2 randomly fail to come up properly. md1 or
md2 come up as inactive and one of the two drivers are marked as spares.
(Why as spares? Why won't it try to run the array with a missing drive?)
While this happens, it's completly abitrary whether sda or sdb is being
used. so md1 can be sda5[2](S) and md2 can be sdb5[2](S).

The (S) is a bit misleading here.  When an array is 'inactive', all devices
are marked as '(S)', because they are not currently active (nothing is as the
whole array is inactive).

When md1 has sda5[2](S), is sdb5 mentioned for md1 as well, or is it simply
absent.   I'm guessing the second.
Yes, i'm 99% sure however it's randomly sda6 or sdb6 that's shown. But never both. Only if I do mdadm -A /dev/md2 /dev/sda6 /dev/sdb6 (after stopping md2 first of course).

This it most likely caused by "mdadm -I" being run by udev on device
discovery.  Possibly it is racing with an "mdadm -A" run from a boot script.
Have a look for a udev/rules.d script which run mdadm -I and maybe disable it
and see what happens.
In init.d I find two scripts calling mdadm. /etc/init.d/mdadm only does monitoring (mdadm --monitor --scan --daemonize) I strongly doubt that forces any of the assembling? (even though scan is there?)

/etc/init.d/mdraid does some md stuff, but that's not run nor enabled.

BTW, I only start md0 from initramfs, so udev apparently does the rest (and sucks at it?)

When this happens, I mdadm --stop /dev/md1 and /dev/md2, followed
immediatly by mdadm -A /dev/md1 (using mdadm.conf which doesn't even
list the devices. ARRAY /dev/md1 metadata=1.2 UUID=nnn name=host:home).
The arrays come up and work just fine.

What happend today however, is that md2 again does not come up, and
sda6[3](S) shows in /proc/mdadm. However re-assembly of the array fails
and only using mdadm -A /dev/md2 /dev/sda6 /dev/sdb6 shows:
mdadm: device 1 in /dev/md2 has wrong state in superblock, but /dev/sdb6
seems ok
mdadm: /dev/md2 assembled from 0 drives and 2 spares - not enough to
start the array.
/proc/mdadm shows as somewhat expected.
md2 : inactive sda6[3](S) sdb6[2](S)

Only using sdb6 however also fails. I guess because it does not want to
use a spare.
mdadm: failed to RUN_ARRAY /dev/md2: Invalid argument
mdadm: Not enough devices to start the array.

Now the really disturbing part comes from mdadm --examine.
valexia oliver # mdadm --examine /dev/sda6
            Magic : a92b4efc
          Version : 1.2
      Feature Map : 0x0
       Array UUID : nnnn
             Name : host:opt  (local to host host)
    Creation Time : Sun Aug 28 17:46:27 2011
       Raid Level : -unknown-
     Raid Devices : 0

   Avail Dev Size : 456165376 (217.52 GiB 233.56 GB)
      Data Offset : 2048 sectors
     Super Offset : 8 sectors
            State : active
      Device UUID : nnnn

      Update Time : Mon May 28 20:52:35 2012
         Checksum : ac17255 - correct
           Events : 1

     Device Role : spare
     Array State :  ('A' == active, '.' == missing)

sdb6 lists identical content only with the checksum's being correbt,
albeit different and of coruse the Device UUID. Array UUID is of course
identical as is creation time.

Also to note, is that grub2 does mention an 'error: Unsupported RAID
level: -1000000.' which probably relates to the 'Raid Level: -unknown-'.

As to what may have caused this? I have absolutely no idea. I did a
clean shutdown where the arrays get cleanly unmounted. Not 100% sure if
the arrays get --stopped but I would be surprised if they did not.

So I guess is this a md driver bug? Is there anything I can do to
recover my data, which i cannot image it not being?

This is a known bug which has been fixed.  You are now running 3.4 so are
safe from it.
Well this strange behavior all stemmed from running 3.2.1. I've only upgraded to 3.4 to see if that 'fixes' it. (It didn't :( unfortunately).

The -100000 error I'm assuming for now also stems from the meta data being corrupt, and will probably go away when trying the below tomorrow :)

You can recover your data by re-creating the array.

   mdadm -C /dev/md2 -l10 -n2 --layout o2 --assume-clean \
   -e 1.2  /dev/sda6 /dev/sdb6

Check that I have that right - don't just assume :-)
That looks very similar to what I used to create the array with, except the assume-clean part. I wonder however, would it not wiser to create the array using /dev/sda6 missing thus creating a degraded array? Atleast I'll still have the sdb6 which MAY contain the data also (since only sda6 'apparently' has wrong state?

Also, would it not be possible to mount sdb6 using the correct offset? I remember raid1 array's could simply be mounted. (with a 2 disk raid10, from what I understand, atleast 1 disk may be mountable?)

when you have created the array, check that the 'Data Offset' is still
correct, then if it is "fsck -n" the array to ensure everything looks good.
Then you should be back in business.
I should then be able to compare it to md1/sda5 and /dev/sdb5. Since md1 and md2 where created with identical settings, they should be almost the same when comparing :)

So to summarize, my array went foobar due to an old known bug and the only way to fix it is to recreate the array, leaving the actual data in place. The FS _should_ start after 2048 sectors on the disk.


Thanks in advance for reading this.

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Thank you so far for your help!
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