RAID5 failed, system drops into limited single mode

English Hardware
1

I have created RAID5 from 3 new 1TB SATA disks using Yast.
RAID is used only for samba file store, the system boots from another single drive
All worked fine only 2 days.

Today I tried starting the system and find the boot failed and there is only a limited shell.

I opened terminal Yast and found that one disk has been removed from the RAID and it is now innactive.

cat /etc/mdadm.conf

DEVICE partitions
ARRAY /dev/md0 level=raid5 UUID= [trim]

cat /proc/mdstat

Personalities
md0 : inactive sdc10 sdd11 sdb13
2930255232 blocks super 1.0

unused devices: none

mdadm --detail /dev/md0

mdadm: md device /dev/md0 does not appear to be active

Checked smartctrl - no errors

What’s happened?
How do I recover the array?
How do I boot the system now?

2

Update

in /var/log/boot.msg found this line:

Starting MD Raid mdadm: /dev/md0 assembled from 2 drives - not enough to start the array while not clean consider --force