root@keruru:/var/log# mdadm --examine /dev/sd[bedc] >> raid.status root@keruru:/var/log# cat raid.status /dev/sdb: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : b1e6af5d:e5848ebe:63727445:2ab99719 Name : keruru:0 (local to host keruru) Creation Time : Fri Jun 30 15:42:27 2017 Raid Level : raid6 Raid Devices : 4 Avail Dev Size : 3906767024 (1862.89 GiB 2000.26 GB) Array Size : 3906765824 (3725.78 GiB 4000.53 GB) Used Dev Size : 3906765824 (1862.89 GiB 2000.26 GB) Data Offset : 262144 sectors Super Offset : 8 sectors State : clean Device UUID : 79e4933f:dfe5923f:5ba03ae7:3efe38eb Update Time : Wed Jul 5 21:06:18 2017 Checksum : 9ff2b025 - correct Events : 119 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 0 Array State : AAAA ('A' == active, '.' == missing) /dev/sdc: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : b1e6af5d:e5848ebe:63727445:2ab99719 Name : keruru:0 (local to host keruru) Creation Time : Fri Jun 30 15:42:27 2017 Raid Level : raid6 Raid Devices : 4 Avail Dev Size : 3906767024 (1862.89 GiB 2000.26 GB) Array Size : 3906765824 (3725.78 GiB 4000.53 GB) Used Dev Size : 3906765824 (1862.89 GiB 2000.26 GB) Data Offset : 262144 sectors Super Offset : 8 sectors State : clean Device UUID : f1e1a946:711886a6:2604780f:8eba4a2d Update Time : Wed Jul 5 21:06:18 2017 Checksum : 784b0046 - correct Events : 119 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 1 Array State : AAAA ('A' == active, '.' == missing) /dev/sdd: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : b1e6af5d:e5848ebe:63727445:2ab99719 Name : keruru:0 (local to host keruru) Creation Time : Fri Jun 30 15:42:27 2017 Raid Level : raid6 Raid Devices : 4 Avail Dev Size : 3906767024 (1862.89 GiB 2000.26 GB) Array Size : 3906765824 (3725.78 GiB 4000.53 GB) Used Dev Size : 3906765824 (1862.89 GiB 2000.26 GB) Data Offset : 262144 sectors Super Offset : 8 sectors State : clean Device UUID : cf3bc8a7:9feed87d:945d8e77:08f7f32d Update Time : Wed Jul 5 21:06:18 2017 Checksum : 197bc63c - correct Events : 119 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 2 Array State : AAAA ('A' == active, '.' == missing) /dev/sde: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : b1e6af5d:e5848ebe:63727445:2ab99719 Name : keruru:0 (local to host keruru) Creation Time : Fri Jun 30 15:42:27 2017 Raid Level : raid6 Raid Devices : 4 Avail Dev Size : 3906767024 (1862.89 GiB 2000.26 GB) Array Size : 3906765824 (3725.78 GiB 4000.53 GB) Used Dev Size : 3906765824 (1862.89 GiB 2000.26 GB) Data Offset : 262144 sectors Super Offset : 8 sectors State : clean Device UUID : b3323d81:279b7c7b:a0c534ed:46d0e6fc Update Time : Wed Jul 5 21:06:18 2017 Checksum : 352daaf4 - correct Events : 119 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 3 Array State : AAAA ('A' == active, '.' == missing) ================ root@keruru:/var/log# mdadm --examine /dev/sd[bedc] | egrep 'Event|/dev/sd' /dev/sdb: Events : 119 /dev/sdc: Events : 119 /dev/sdd: Events : 119 /dev/sde: Events : 119 =============== root@keruru:/var/log# mdadm --stop /dev/md0 mdadm: stopped /dev/md0 root@keruru:/var/log# mdadm --assemble --force /dev/md0 /dev/sdb /dev/sde /dev/sdd /dev/sdc mdadm: /dev/md0 has been started with 4 drives. root@keruru:/var/log# cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] md0 : active (auto-read-only) raid6 sdb[4] sde[3] sdd[2] sdc[1] 3906765824 blocks super 1.2 level 6, 512k chunk, algorithm 2 [4/4] [UUUU] unused devices: =============== root@keruru:/var/log# grep Role raid.status Device Role : Active device 0 Device Role : Active device 1 Device Role : Active device 2 Device Role : Active device 3 =============== root@keruru:/var/log# grep Used raid.status Used Dev Size : 3906765824 (1862.89 GiB 2000.26 GB) Used Dev Size : 3906765824 (1862.89 GiB 2000.26 GB) Used Dev Size : 3906765824 (1862.89 GiB 2000.26 GB) Used Dev Size : 3906765824 (1862.89 GiB 2000.26 GB) =============== root@keruru:/var/log# mdadm --create --assume-clean --level=6 --raid-devices=4 --size=1953382912 /dev/md0 /dev/sdb /dev/sde /dev/sdd /dev/sdc mdadm: /dev/sdb appears to be part of a raid array: level=raid6 devices=4 ctime=Fri Jun 30 15:42:27 2017 mdadm: partition table exists on /dev/sdb but will be lost or meaningless after creating array mdadm: /dev/sde appears to be part of a raid array: level=raid6 devices=4 ctime=Fri Jun 30 15:42:27 2017 mdadm: /dev/sdd appears to be part of a raid array: level=raid6 devices=4 ctime=Fri Jun 30 15:42:27 2017 mdadm: /dev/sdc appears to be part of a raid array: level=raid6 devices=4 ctime=Fri Jun 30 15:42:27 2017 Continue creating array? n mdadm: create aborted. =============== root@keruru:/var/log# mdadm --create --assume-clean --level=6 --raid-devices=4 --size=1953382912 /dev/md0 /dev/sdb /dev/sde /dev/sdd /dev/sdc mdadm: /dev/sdb appears to be part of a raid array: level=raid6 devices=4 ctime=Fri Jun 30 15:42:27 2017 mdadm: partition table exists on /dev/sdb but will be lost or meaningless after creating array mdadm: /dev/sde appears to be part of a raid array: level=raid6 devices=4 ctime=Fri Jun 30 15:42:27 2017 mdadm: /dev/sdd appears to be part of a raid array: level=raid6 devices=4 ctime=Fri Jun 30 15:42:27 2017 mdadm: /dev/sdc appears to be part of a raid array: level=raid6 devices=4 ctime=Fri Jun 30 15:42:27 2017 Continue creating array? y mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md0 started. =============== root@keruru:/# mount -t ext4 /dev/md0 /mnt/md0 mount: wrong fs type, bad option, bad superblock on /dev/md0, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so =============== root@keruru:/# dmesg | tail [448318.800806] --- level:6 rd:4 wd:4 [448318.800812] disk 0, o:1, dev:sdb [448318.800817] disk 1, o:1, dev:sde [448318.800822] disk 2, o:1, dev:sdd [448318.800827] disk 3, o:1, dev:sdc [448318.800951] md0: detected capacity change from 0 to 4000528203776 [448318.809375] md0: unknown partition table [448358.704189] EXT4-fs (md0): Unrecognized mount option "\x08" or missing value [448358.706680] EXT4-fs (md0): failed to parse options in superblock: \x08 [448358.706690] EXT4-fs (md0): Number of reserved GDT blocks insanely large: 9216 =============== Jul 11 17:23:15 keruru kernel: [447719.812775] md: export_rdev(sdd) Jul 11 17:23:19 keruru kernel: [447724.396327] md: md0 stopped. Jul 11 17:23:19 keruru kernel: [447724.400278] md: bind Jul 11 17:32:29 keruru kernel: [448273.001687] md0: detected capacity change from 4000528203776 to 0 Jul 11 17:32:29 keruru kernel: [448273.001714] md: md0 stopped. Jul 11 17:32:29 keruru kernel: [448273.001729] md: unbind Jul 11 17:32:29 keruru kernel: [448273.022972] md: export_rdev(sdc) Jul 11 17:32:29 keruru kernel: [448273.023143] md: unbind Jul 11 17:32:29 keruru kernel: [448273.054889] md: export_rdev(sde) Jul 11 17:32:29 keruru kernel: [448273.055035] md: unbind Jul 11 17:32:29 keruru kernel: [448273.086870] md: export_rdev(sdd) Jul 11 17:33:14 keruru kernel: [448318.800827] disk 3, o:1, dev:sdc ===============