Re: RAID 6, 6 device array - all devices lost superblock

John Stoffel
2022-09-02T19:12:37Z

>>>>> "Peter" == Peter Sanders <plsander@gmail.com> writes:

Peter, please include the output of all the commands, not just the
commands themselves. See my comments below.

> Question on restarting from scratch...
> How to reset to the starting point?

I think you need to blow away the loop devices and re-create them.

Or at least blow away the dmsetup devices you just created.

It might be quickest to just reboot. What OS are you using for the
recovery? Is it a recent live image? Sorry for asking so many
questions... some of this is new to me too.

> dmsetup, both for remove and create of the overlay seems to be hanging.

> On Fri, Sep 2, 2022 at 10:56 AM Peter Sanders <plsander@gmail.com> wrote:
>>
>> contents of /proc/mdstat
>>
>> root@superior:/mnt/backup# cat /proc/mdstat
>> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
>> [raid4] [raid10]
>> unused devices: <none>
>> root@superior:/mnt/backup#
>>
>>
>>
>> Here are the steps I ran (minus some mounting other devices and
>> looking around for mdadm tracks on the old os disk)
>>
>> 410 DEVICES=$(cat /proc/partitions | parallel --tagstring {5}
>> --colsep ' +' mdadm -E /dev/{5} |grep $UUID | parallel --colsep '\t'
>> echo /dev/{1})
>> 411 apt install parallel
>> 412 DEVICES=$(cat /proc/partitions | parallel --tagstring {5}
>> --colsep ' +' mdadm -E /dev/{5} |grep $UUID | parallel --colsep '\t'
>> echo /dev/{1})
>> 413 echo $DEVICES

So you found no MD RAID super blocks on any of the base devices. You
can skip this step moving forward.

>> 414 cat /proc/partitions
>> 415 DEVICES=/dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sdg
>> 416 DEVICES="/dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sdg"
>> 417 echo $DEVICES
>> 418 parallel 'test -e /dev/loop{#} || mknod -m 660 /dev/loop{#} b 7
>> {#}' ::: $DEVICES
>> 419 ls /dev/loop*

Can you show the output of all these commands, not just the commands please?

>> 423 parallel truncate -s300G overlay-{/} ::: $DEVICES

>> 427 parallel 'size=$(blockdev --getsize {}); loop=$(losetup -f
>> --show -- overlay-{/}); echo 0 $size snapshot {} $loop P 8 | dmsetup
>> create {/}' ::: $DEVICES
>> 428 ls /dev/mapper/

This is some key output to view.

>> 429 OVERLAYS=$(parallel echo /dev/mapper/{/} ::: $DEVICES)
>> 430 echo $OVERLAYS

What are the overlays?

>> 431 dmsetup status

What did this command show?

>> 432 mdadm --assemble --force /dev/md1 $OVERLAYS

And here is where I think you need to put --assume-clean when using
'create' command instead. It's not going to assemble anything because
the info was wiped. I *think* you really want:

mdadm --create /dev/md1 --level=raid6 -n 6 --assume-clean $OVERLAYS

And once you do this above command and it comes back, do:

cat /proc/mdstat

and show all the output please!

>> 433 history
>> 434 dmsetup status
>> 435 echo $OVERLAYS
>> 436 mdadm --assemble --force /dev/md0 $OVERLAYS
>> 437 cat /proc/partitions
>> 438 mkdir /mnt/oldroot
>> << look for inird mdadm files >>
>> 484 echo $OVERLAYS
>> 485 mdadm --create /dev/md0 --level=raid6 -n 6 /dev/mapper/sdb
>> /dev/mapper/sdc /dev/mapper/sdd /dev/mapper/sde /dev/mapper/sdf
>> /dev/mapper/sdg

I'm confused here, what is the difference between the md1 you
assembled above, and the md0 you're doing here?

>> << cancelled out of 485, review instructions... >>
>> 486 mdadm --create /dev/md0 --level=raid6 -n 6 /dev/mapper/sdb
>> /dev/mapper/sdc /dev/mapper/sdd /dev/mapper/sde /dev/mapper/sdf
>> /dev/mapper/sdg
>> 487 fsck -n /dev/md0

And what output did you get here? Did it find a filesystem? You might want
to try:

blkid /dev/md0

>> 488 mdadm --stop /dev/md0
>> 489 echo $DEVICES
>> 490 parallel 'dmsetup remove {/}; rm overlay-{/}' ::: $DEVICES
>> 491 dmsetup status

This all worked properly? No errors?

I gave up after this because it's not clear what the results really
are. If you don't find a filesystem that fsck's cleanly, then you
should just need to stop the array, then re-create it but shuffle the
order of the devices.

Instead of disk in order of "sdb sdc sdd... sdN", you would try the
order "sdc sdd ... sdN sdb". See how I moved sdb to the end of the
list of devices? With six disks, you have I think 6 factorial options
to try. Which is alot of options to go though, and why you need to
automate this more. But also keep a log and show the output!

John

>> 492 ls
>> 493 rm overlay-*
>> 494 ls
>> 495 parallel losetup -d ::: /dev/loop[0-9]*
>> 496 parallel 'test -e /dev/loop{#} || mknod -m 660 /dev/loop{#} b 7
>> {#}' ::: $DEVICES
>> 497 parallel truncate -s300G overlay-{/} ::: $DEVICES
>> 498 parallel 'size=$(blockdev --getsize {}); loop=$(losetup -f
>> --show -- overlay-{/}); echo 0 $size snapshot {} $loop P 8 | dmsetup
>> create {/}' ::: $DEVICES
>> 499 dmsetup status
>> 500 /sbin/reboot
>> 501 history
>> 502 dmsetup status
>> 503 mount
>> 504 cat /proc/partitions
>> 505 nano /etc/fstab
>> 506 mount /mnt/backup/
>> 507 ls /mnt/backup/
>> 508 rm /mnt/backup/
>> 509 rm /mnt/backup/overlay-sd*
>> 510 emacs setupOverlay &
>> 511 ps auxww | grep emacs
>> 512 kill 65017
>> 513 ls /dev/loo*
>> 514 DEVICES='/dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sdg'
>> 515 echo $DEVICES
>> 516 parallel 'test -e /dev/loop{#} || mknod -m 660 /dev/loop{#} b
>> 7 {#}' ::: $DEVICES
>> 517 ls /dev/loo*
>> 518 parallel truncate -s4000G overlay-{/} ::: $DEVICES
>> 519 ls
>> 520 rm overlay-sd*
>> 521 cd /mnt/bak
>> 522 cd /mnt/backup/
>> 523 ls
>> 524 parallel truncate -s4000G overlay-{/} ::: $DEVICES
>> 525 ls -la
>> 526 blockdev --getsize /dev/sdb
>> 527 man losetup
>> 528 man losetup
>> 529 parallel 'size=$(blockdev --getsize {}); loop=$(losetup -f
>> --show -- overlay-{/}); echo 0 $size snapshot {} $loop P 8 | dmsetup
>> create {/}' ::: $DEVICES
>> 530 dmsetup status
>> 531 history | grep mdadm
>> 532 history
>> 533 dmsetup status
>> 534 history | grep dmsetup
>> 535 dmsetup status
>> 536 dmsetup remove sdg
>> 537 dmsetup ls --tree
>> 538 lsof
>> 539 dmsetup ls --tre
>> 540 dmsetup ls --tree
>> 541 lsof | grep -i sdg
>> 542 lsof | grep -i sdf
>> 543 history |grep dmsetup | less
>> 544 dmsetup status
>> 545 history > ~plsander/Documents/raidIssues/joblog
>>
>> On Wed, Aug 31, 2022 at 4:37 PM John Stoffel <john@stoffel.org> wrote:
>> >
>> > >>>>> "Peter" == Peter Sanders <plsander@gmail.com> writes:
>> >
>> > > encountering a puzzling situation.
>> > > dmsetup is failing to return.
>> >
>> > I don't think you need to use dmsetup in your case, but can you post
>> > *all* the commands you ran before you got to this point, and the
>> > output of
>> >
>> > cat /proc/mdstat
>> >
>> > as well? Thinking on this some more, you might need to actually also
>> > add:
>> >
>> > --assume-clean
>> >
>> > to the 'mdadm create ....' string, since you don't want it to zero the
>> > array or anything.
>> >
>> > Sorry for not remembering this at the time!
>> >
>> > So if you can, please just start over from scratch, showing the setup
>> > of the loop devices, the overlayfs setup, and the building the RAID6
>> > array, along with the cat /proc/mdstat after you do the initial build.
>> >
>> > John
>> >
>> > P.S. For those who hated my email citing tool, I pulled it out for
>> > now. Only citing with > now. :-)
>> >
>> > > root@superior:/mnt/backup# dmsetup status
>> > > sdg: 0 5860533168 snapshot 16/8388608000 16
>> > > sdf: 0 5860533168 snapshot 16/8388608000 16
>> > > sde: 0 5860533168 snapshot 16/8388608000 16
>> > > sdd: 0 5860533168 snapshot 16/8388608000 16
>> > > sdc: 0 5860533168 snapshot 16/8388608000 16
>> > > sdb: 0 5860533168 snapshot 16/8388608000 16
>> >
>> > > dmsetup remove sdg runs for hours.
>> > > Canceled it, ran dmsetup ls --tree and find that sdg is not present in the list.
>> >
>> > > dmsetup status shows:
>> > > sdf: 0 5860533168 snapshot 16/8388608000 16
>> > > sde: 0 5860533168 snapshot 16/8388608000 16
>> > > sdd: 0 5860533168 snapshot 16/8388608000 16
>> > > sdc: 0 5860533168 snapshot 16/8388608000 16
>> > > sdb: 0 5860533168 snapshot 16/8388608000 16
>> >
>> > > dmsetup ls --tree
>> > > root@superior:/mnt/backup# dmsetup ls --tree
>> > > sdf (253:3)
>> > > ├─ (7:3)
>> > > └─ (8:80)
>> > > sde (253:1)
>> > > ├─ (7:1)
>> > > └─ (8:64)
>> > > sdd (253:2)
>> > > ├─ (7:2)
>> > > └─ (8:48)
>> > > sdc (253:0)
>> > > ├─ (7:0)
>> > > └─ (8:32)
>> > > sdb (253:5)
>> > > ├─ (7:5)
>> > > └─ (8:16)
>> >
>> > > any suggestions?
>> >
>> >
>> >
>> > > On Tue, Aug 30, 2022 at 2:03 PM Wols Lists <antlists@youngman.org.uk> wrote:
>> > >>
>> > >> On 30/08/2022 14:27, Peter Sanders wrote:
>> > >> >
>> > >> > And the victory conditions would be a mountable file system that passes a fsck?
>> > >>
>> > >> Yes. Just make sure you delve through the file system a bit and satisfy
>> > >> yourself it looks good, too ...
>> > >>
>> > >> Cheers,
>> > >> Wol