CentOS - Apr 2019 - Kernel panic after removing SW RAID1 partitions, setting up ZFS.

System is CentOS 6 all up to date, previously had two drives in MD RAID 
configuration. 

md0: sda1/sdb1, 20 GB, OS / Partition
md1: sda2/sdb2, 1 TB, data mounted as /home 

Installed kmod ZFS via yum, reboot, zpool works fine. Backed up the /home data 
2x, then stopped the sd[ab]2 partition with: 

mdadm --stop /dev/md1; 
mdadm --zero-superblock /dev/sd[ab]1; 

Removed /home in /etc/fstab. Used fdisk to set the partition type to gpt for 
sda2 and sdb2, then built *then destroyed* a ZFS mirror pool using the two 
partitions. 

Now the system won't boot, has a kernel panic. I'm remote, so I'll
be going in
tomorrow to see what's up. My assumption is that it has something to do with
mdadm/RAID not being "fully removed". 

Any idea what I might have missed? 

Here's a screenshot of the panic
http://effortlessis.com/images/IMG_0705.JPG

In article <6566355.ijNRhnPfCt at tesla.schoolpathways.com>,
Benjamin Smith <lists at benjamindsmith.com>
wrote:
> System is CentOS 6 all up to date, previously had two drives in MD RAID 
> configuration. 
> 
> md0: sda1/sdb1, 20 GB, OS / Partition
> md1: sda2/sdb2, 1 TB, data mounted as /home 
> 
> Installed kmod ZFS via yum, reboot, zpool works fine. Backed up the /home
data
> 2x, then stopped the sd[ab]2 partition with: 
> 
> mdadm --stop /dev/md1; 
> mdadm --zero-superblock /dev/sd[ab]1; 
Did you mean /dev/sd[ab]2 instead?
> Removed /home in /etc/fstab. Used fdisk to set the partition type to gpt
for
> sda2 and sdb2, then built *then destroyed* a ZFS mirror pool using the two 
> partitions. 
> 
> Now the system won't boot, has a kernel panic. I'm remote, so
I'll be going in
> tomorrow to see what's up. My assumption is that it has something to do
with
> mdadm/RAID not being "fully removed". 
> 
> Any idea what I might have missed? 
I think it's because you clobbered md0 when you did --zero-superblock on
sd[ab]1
instead of 2.

Don't you love it when some things count from 0 and others from 1?

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org

> In article <6566355.ijNRhnPfCt at tesla.schoolpathways.com>,
> Benjamin Smith <lists at benjamindsmith.com> wrote:
>> System is CentOS 6 all up to date, previously had two drives in MD RAID
>> configuration.
>>
>> md0: sda1/sdb1, 20 GB, OS / Partition
>> md1: sda2/sdb2, 1 TB, data mounted as /home
>>
>> Installed kmod ZFS via yum, reboot, zpool works fine. Backed up the
>> /home data
>> 2x, then stopped the sd[ab]2 partition with:
>>
>> mdadm --stop /dev/md1;
>> mdadm --zero-superblock /dev/sd[ab]1;
>
> Did you mean /dev/sd[ab]2 instead?
>
>> Removed /home in /etc/fstab. Used fdisk to set the partition type to
gpt
>> for
>> sda2 and sdb2, then built *then destroyed* a ZFS mirror pool using the
>> two
>> partitions.
>>
>> Now the system won't boot, has a kernel panic. I'm remote, so
I'll be
>> going in
>> tomorrow to see what's up. My assumption is that it has something
to do
>> with
>> mdadm/RAID not being "fully removed".
>>
>> Any idea what I might have missed?
>
> I think it's because you clobbered md0 when you did --zero-superblock
on
> sd[ab]1
> instead of 2.
>
> Don't you love it when some things count from 0 and others from 1?
That's really a problem but difficult to fix I guess. IMHO it's better
to
keep things the way they are as long as the solution is not really better
than the old behavior. Maybe the new Linux Ethernet naming scheme can
serve as a bad example if you ask me.

But here, mdadm could have done better: --zero-superblock checks if the
device contains a valid md superblock, but it fails to also check if the
device belongs to a running md device :-(

If it turns out that this is your problem, maybe you could ask the mdadm
developers to improve it?

Regards,
Simon