Found the solution, but it is odd.
Both following commands mount the RAID 10, but LVM2 mounts
(automatically) only when the second form is used.
mdadm --verbose --assemble /dev/md0 # RAID 10 assembled, but no LVM2.
mdadm --verbose --assemble /dev/md/0 # RAID 10 assembled, LVM2 works.
I find this a bit disappointing. I do not understand the "magic" behind
this kind of behaviour and I wish there were commands to tell LVM2 to
look and find the physical volume in "md0". Comments are welcomed.
I send my thanks to Chris Murphy for his response.
Best regards,
Hans Deragon
P.S. Sorry for the long delay between posts; it took me a while to find
this out.
On 2018-06-05 09:34 PM, Hans Deragon wrote:
> Greetings,
>
> Under Linux Kernel 4.4.0-127-generic, Ubuntu 16.04 LTS Xenial Xerus, I
> successfully created a healthy raid10 using 4x4Tib, LVM2 and ext4.
>
> When I boot into a USB keyfob installed with Ubuntu 18.04 LTS Bionic
> Beaver, Linux Kernel 4.15.0-20-generic #21-Ubuntu SMP, the system cannot
> find the LVM2 physical volume.
>
> Under Ubuntu 18.04 (USB keyfob), I run:
>
> $ apt install mdadm
> ...
> $ mdadm --verbose --assemble /dev/md0 # Works!
> $ cat /proc/mdstat # Shows raid.
> Personalities : [raid10] [linear] [multipath] [raid0] [raid1] [raid6]
> [raid5] [raid4]
> md0 : active raid10 sdh[0] sdb[1] sdc[2] sdd[3]
> 7813774336 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
> bitmap: 0/59 pages [0KB], 65536KB chunk
>
> $ pvscan # Shows nothing!
> $
>
> Why can't pvscan find the physical volume? Remember, this is a %100
> healthy working RAID10. If I remove the USB keyfob and reboot into my
> Ubuntu 16.04 LTS system, the whole drive (ext4) gets automatically
> mounted properly, all the time without any errors. It works flawlessly
> under Linux Kernel 4.4.0-127-generic, but not with Linux Kernel
> 4.15.0-20-generic #21.
>
> On the web, I find only people having defective RAIDs when pvscan
> returns nothing. Is there a way to force pvscan/LVM2 to consider /dev/md0?
>
> Unfortunately, I cannot upgrade to Ubuntu 18.04/Linux Kernel 4.15.0
> until this is resolved.
>
> Best regards,
> Hans Deragon
>
Attachment:
signature.asc
Description: OpenPGP digital signature
