[linux-lvm] Every now and then LVM is not recognized - LVM2 on RAID10

[exxs.net - matevz sernc-urban]

Dear LVM-Users,

i am running into a very interesting situation today, that our LVM 
metadata is recognized only sometimes. LVM was running fine for some 
weeks and now from today on running pvscan 10 times one after another i 
get about 4 positive and 6 negative results (its somehow a coincidence 
that LVM is recognized).

* WORKING STATE:
server$ pvscan
   PV /dev/md2   VG mainvg   lvm2 [909.59 GB / 299.59 GB free]
   Total: 1 [909.59 GB] / in use: 1 [909.59 GB] / in no VG: 0 [0   ]

* NOT-WORKING STATE:
server$ pvscan
   No matching physical volumes found

notice: Same behaviour with vgscan and lvscan.

Our Setup:
* RAID-10 /dev/md2 on /dev/sd[a-d]5
cat /proc/mdstat
Personalities : [raid1] [raid10]
md2 : active raid10 sdb5[1] sda5[0] sdd5[3] sdc5[2]
       953778688 blocks 64K chunks 2 far-copies [4/4] [UUUU]

* LVM2 on top of /dev/md2 (no separate lvm partition)
lvm metadata backup is present and it is exactly the same as backups we 
did months ago

I will attach the lvm2 metadata file to this message (vg name: mainvg)

WORKING STATE:
server$ pvscan -vv
       Setting global/locking_type to 1
       File-based locking selected.
       Setting global/locking_dir to /var/lock/lvm
       Locking /var/lock/lvm/P_global WB
     Wiping cache of LVM-capable devices
       /dev/sndstat: stat failed: No such file or directory
     Wiping internal VG cache
     Walking through all physical volumes
       /dev/md2: size is 1907557376 sectors
       /dev/md2: lvm2 label detected
   PV /dev/md2   VG mainvg   lvm2 [909.59 GB / 299.59 GB free]
   Total: 1 [909.59 GB] / in use: 1 [909.59 GB] / in no VG: 0 [0   ]
       Unlocking /var/lock/lvm/P_global

NOT-WORKING STATE:
server$ pvscan -vv
       Setting global/locking_type to 1
       File-based locking selected.
       Setting global/locking_dir to /var/lock/lvm
       Locking /var/lock/lvm/P_global WB
     Wiping cache of LVM-capable devices
       /dev/sndstat: stat failed: No such file or directory
     Wiping internal VG cache
     Walking through all physical volumes
       /dev/md2: size is 1907557376 sectors
       /dev/md2: No label detected
   No matching physical volumes found
       Unlocking /var/lock/lvm/P_global


Any hints?

Where should it look regarding "/dev/md2: No label detected" vs. 
"/dev/md2: lvm2 label detected"??

It seems like RAID-10 is not sync'ed well maybe? But, mdstat reports all 
disks are up.

Thanks for your help.
Mat
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