[CentOS] Problem with softwareraid

Fri Aug 18 19:35:48 UTC 2017
Mr Typo <euroregistrar at gmail.com>

Hello all,

i have already had a discussion on the software raid mailinglist and i
want to switch to this one :)

I am having a really strange problem with my md0 device running
centos7. after a new start of my server the md0 was gone. now after
trying to find the problem i detected the following:

Booting any installed kernel gives me NO md0 device. (ls /dev/md*
doesnt give anything). a 'cat /proc/partitions show me now
/dev/sd[a-d]1 partition. partprobe and a mdadm assemble gives me "disk

[root at quad live]# cat mdstat
Personalities : [raid6] [raid5] [raid4] [raid10]
unused devices: <none>

[root at quad ~]# partprobe
device-mapper: remove ioctl on WDC_WD20EFRX-68AX9N0_WD-WMC301255087p1
failed: Device or resource busy
Warning: parted was unable to re-read the partition table on
/dev/mapper/WDC_WD20EFRX-68AX9N0_WD-WMC301255087 (Device or resource
busy).  This means Linux won't know anything about the modifications
you made.

[root at quad ~]# mdadm --assemble --force /dev/md0 /dev/sda1 /dev/sdb1
/dev/sdc1 /dev/sdd1
mdadm: /dev/sda1 is busy - skipping
mdadm: /dev/sdb1 is busy - skipping
mdadm: /dev/sdc1 is busy - skipping
mdadm: /dev/sdd1 is busy - skipping

booting from a usb stick for rescue my centos everything works. the
md0 device exists and is mounted. (rw).

[root at quad usb-rescue]# cat mount  | grep '/data'
/dev/mapper/data-store on /mnt/sysimage/store type xfs
/dev/mapper/data-tm on /mnt/sysimage/var/lib/vdr/video type xfs

3rd option: i am booting the installed rescue kernel from disk:
i am getting a md0 device, but its not started. when i stop the md0 i
cant assemble it anymore (disk busy)

        Version : 1.2
  Creation Time : Wed Aug 20 19:28:52 2014
     Raid Level : raid5
  Used Dev Size : 1953382272 (1862.89 GiB 2000.26 GB)
   Raid Devices : 4
  Total Devices : 4
    Persistence : Superblock is persistent

    Update Time : Thu Aug 17 22:38:14 2017
          State : active, Not Started
 Active Devices : 4
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 128K

           Name : quad.core.sartori.at:0  (local to host quad.core.sartori.at)
           UUID : 9d020f27:c0542472:b95a18d2:5741114d
         Events : 25458

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       8       17        1      active sync   /dev/sdb1
       2       8       33        2      active sync   /dev/sdc1
       4       8       49        3      active sync   /dev/sdd1

anyone got an idea, in which direction the problem could be? more logs
needed? please help, i have no ideas anymore.