Script started on Fr 18 Nov 2016 21:50:01 CET
zoey# mkdir overlays
zoey# cd overlays
zoey# for i in sd{b,c1,d1}; do truncate -r /dev/$i f_$i; done
zoey# ls -l
insgesamt 24
-rw-r--r-- 1 root root 4000787030016 Nov 18 21:52 f_sdb
-rw-r--r-- 1 root root 4000785104896 Nov 18 21:52 f_sdc1
-rw-r--r-- 1 root root 4000785104896 Nov 18 21:52 f_sdd1
zoey# for i in sd{b,c1,d1}; do printf '%s\n' "0 $(blockdev --getsz /dev/$i) snapshot /dev/$i $(losetup -f --show f_$i) P 8" | dmsetup create o_$i; done
zoey# ls -l /dev/mapper
insgesamt 0
crw------- 1 root root 10, 236 Nov 18 21:52 control
lrwxrwxrwx 1 root root       7 Nov 18 21:52 o_sdb -> ../dm-0
lrwxrwxrwx 1 root root       7 Nov 18 21:52 o_sdc1 -> ../dm-1
lrwxrwxrwx 1 root root       7 Nov 18 21:52 o_sdd1 -> ../dm-2
zoey# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
unused devices: <none>
zoey# mdadm --assemble /dev/md0 --verbose /dev/mapper/o_sdb /dev/mapper/o_sdc1 /dev/mapper/o_sdd1
mdadm: looking for devices for /dev/md0
mdadm: /dev/mapper/o_sdb is identified as a member of /dev/md0, slot 0.
mdadm: /dev/mapper/o_sdc1 is identified as a member of /dev/md0, slot 1.
mdadm: /dev/mapper/o_sdd1 is identified as a member of /dev/md0, slot 2.
mdadm: failed to add /dev/mapper/o_sdc1 to /dev/md0: Invalid argument
mdadm: failed to add /dev/mapper/o_sdd1 to /dev/md0: Invalid argument
mdadm: added /dev/mapper/o_sdb to /dev/md0 as 0
mdadm: /dev/md0 assembled from 1 drive - need all 3 to start it (use --run to insist).
zoey# mdadm --assemble /dev/md0 --verbose /dev/mapper/o_sdb /dev/mapper/o_sdc1 /dev/mapper/o_sdd1 --force
mdadm: looking for devices for /dev/md0
mdadm: /dev/mapper/o_sdb is identified as a member of /dev/md0, slot 0.
mdadm: /dev/mapper/o_sdc1 is identified as a member of /dev/md0, slot 1.
mdadm: /dev/mapper/o_sdd1 is identified as a member of /dev/md0, slot 2.
mdadm: failed to add /dev/mapper/o_sdc1 to /dev/md0: Invalid argument
mdadm: failed to add /dev/mapper/o_sdd1 to /dev/md0: Invalid argument
mdadm: added /dev/mapper/o_sdb to /dev/md0 as 0
mdadm: failed to RUN_ARRAY /dev/md0: Input/output error
zoey# mdadm --create /dev/md0 --level 5 --raid-devices 3 --assume-clean /dev/mapper/o_sdb /dev/mapper/o_sdc1 /dev/mapper/o_sdd1
mdadm: /dev/mapper/o_sdb appears to be part of a raid array:
       level=raid5 devices=3 ctime=Fri Sep 26 17:23:15 2014
mdadm: /dev/mapper/o_sdc1 appears to be part of a raid array:
       level=raid5 devices=3 ctime=Fri Sep 26 17:23:15 2014
mdadm: /dev/mapper/o_sdd1 appears to be part of a raid array:
       level=raid5 devices=3 ctime=Fri Sep 26 17:23:15 2014
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
zoey# ls /dev/md*
/dev/md0

/dev/md:
zoey# blkid /dev/md0
zoey# head -c 2048 /dev/md0 |file -
/dev/stdin: data
zoey# mdadm --stop /dev/md0
mdadm: stopped /dev/md0
zoey# exit

Script done on Fr 18 Nov 2016 21:57:31 CET