Re: "md/raid:mdX: cannot start dirty degraded array."

Andreas,

LVM RAID and MD RAID have different, hence incompatible superblock formats
so you can't switch to MD in this case.

Try activating your RaidLV with 'lvchange -ay --activationmode=degraded
/dev/vg_ssds_0/host-home', add a replacement PV of adequate size if none
available and run 'lvconvert --repair /dev/vg_ssds_0/host-home'.

Best,
Heinz

On Fri, Oct 29, 2021 at 1:07 PM Andreas Trottmann <
[email protected]> wrote:

> Am 11.10.21 um 16:08 schrieb Andreas Trottmann:
>
> > I am running a server that runs a number of virtual machines and manages
> their virtual disks as logical volumes using lvmraid (...)
>
> > After a restart, all of the logical volumes came back, except one.
>
> > When I'm trying to activate it, I get:
> >
> > # lvchange -a y /dev/vg_ssds_0/host-home
> >    Couldn't find device with uuid 8iz0p5-vh1c-kaxK-cTRC-1ryd-eQd1-wX1Yq9.
> >    device-mapper: reload ioctl on  (253:245) failed: Input/output error
>
>
> I am replying to my own e-mail here in order to document how I got the
> data back, in case someone in a similar situation finds this mail when
> searching for the symptoms.
>
> First: I did *not* succeeed in activating the lvmraid volume. No matter
> how I tried to modify the _rmeta volumes, I always got "reload ioctl
> (...) failed: Input/output error" from "lvchange", and "cannot start
> dirty degraded array" in dmesg.
>
> So, I used "lvchange -a y /dev/vg_ssds_0/host-home_rimage_0" (and
> _rimage_2 and _rimage_3, as those were the ones that were *not* on the
> failed PV) to get access to the indivdual RAID SubLVs. I then used "dd
> if=/dev/vg_ssds_0/host-home_rimage_0 of=/mnt/space/rimage_0" to copy the
> data to a file on a filesystem with enough space. I repeated this with 2
> and 3 as well. I then used losetup to access /mnt/space/rimage_0 as
> /dev/loop0, rimage_2 as loop2, and rimage_3 as loop3.
>
> Now I wanted to use mdadm to "build" the RAID in the "array that doesn't
> have per-device metadata (superblocks)" case:
>
> # mdadm --build /dev/md0 -n 4 -c 128 -l 5 --assume-clean --readonly
> /dev/loop0 missing /dev/loop2 /dev/loop3
>
> However, this failed with "mdadm: Raid level 5 not permitted with --build".
>
> ("-c 128" was the chunk size used when creating the lvmraid, "-n 4" and
> "-l 5" refer to the number of devices and the raid level)
>
> I then read the man page about the "superblocks", and found out that the
> "1.0" style of RAID metadata (selected with an mdadm "-e 1.0" option)
> places a superblock at the end of the device. Some experimenting on
> unused devices showed that the size used for actual data was the size of
> the block device minus 144 KiB (possibly 144 KiB = 128 KiB (chunksize) +
> 8 KiB (size of superblock) + 8 KiB (size of bitmap). So I added 147456
> zero bytes at the end of each file:
>
> # for i in 0 2 3; do head -c 147456 /dev/zero >> /mnt/space/rimage_$i; done
>
> After detaching and re-attaching the loop devices, I ran
>
> # mdadm --create /dev/md0 -n 4 -c 128 -l 5 -e 1.0 --assume-clean
> /dev/loop0 missing /dev/loop2 /dev/loop3
>
> (substituting "missing" in the place where the missing RAID SubLV would
> have been)
>
> And, voilà: /dev/md0 was perfectly readable, fsck showed no errors, and
> it could be mounted correctly, with all data intact.
>
>
>
> Kind regards
>
> --
> Andreas Trottmann
> Werft22 AG
> Tel    +41 (0)56 210 91 32
> Fax    +41 (0)56 210 91 34
> Mobile +41 (0)79 229 88 55
>
>
> _______________________________________________
> linux-lvm mailing list
> [email protected]
> https://listman.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

_______________________________________________
linux-lvm mailing list
[email protected]
https://listman.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/