The mdadm command comes from the abbreviation of the English phrase "multiple devices admin", and its function is to manage RAID disk array groups. As a management tool for soft RAID devices under the Linux system, the mdadm command can perform a full set of management operations such as creation, adjustment, monitoring, and deletion.
Syntax format: mdadm [parameter] device name
Parameter Encyclopedia
-D Display detailed information of the RAID device
-A Join a previously defined RAID
-l specifies the RAID level
-n specifies the number of active devices in the RAID
-f List the RAID member as faulty so that it can be removed
-r Move the RAID member out of the RAID device
-a Add a member to the RAID device
-S Disable the RAID device and release all resources
-x specifies the number of spare members for the initial RAID device
First create four partitions
[root@compute ~]# mdadm -C /dev/md7 -n 3 -l 5 -x 1 /dev/sde{1,2,3,4}
mdadm: /dev/sde1 appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Mar 7 17:24:53 2023
mdadm: /dev/sde2 appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Mar 7 17:24:53 2023
mdadm: /dev/sde3 appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Mar 7 17:24:53 2023
mdadm: /dev/sde4 appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Mar 7 17:24:53 2023
mdadm: largest drive (/dev/sde4) exceeds size (2094080K) by more than 1%
Continue creating array? y
mdadm: Fail create md7 when using /sys/module/md_mod/parameters/new_array
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md7 started.
sde 8:64 0 10G 0 disk ├─sde1 8:65 0 2G 0 part │ └─md7 9:7 0 4G 0 raid5 ├─sde2 8:66 0 2G 0 part │ └─md7 9:7 0 4G 0 raid5 ├─sde3 8:67 0 2G 0 part │ └─md7 9:7 0 4G 0 raid5 └─sde4 8:68 0 4G 0 part └─md7 9:7 0 4G 0 raid5
[root@compute ~]# mdadm -D /dev/md7
/dev/md7:
Version : 1.2
Creation Time : Tue Mar 7 17:29:25 2023
Raid Level : raid5
Array Size : 4188160 (3.99 GiB 4.29 GB)
Used Dev Size : 2094080 (2045.00 MiB 2144.34 MB)
Raid Devices : 3
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Tue Mar 7 17:29:36 2023
State : clean
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 512K
Consistency Policy : resync
Name : compute:7 (local to host compute)
UUID : dcdfacfb:9b2f17cd:ce176b58:9e7c56a4
Events : 18
Number Major Minor RaidDevice State
0 8 65 0 active sync /dev/sde1
1 8 66 1 active sync /dev/sde2
4 8 67 2 active sync /dev/sde3
3 8 68 - spare /dev/sde4
mdadm -S /dev/md7 //Stop the array group with one hard disk at one time
[root@compute ~]# mdadm -C /dev/md7 -x 1 -n 3 -l 5 /dev/sdd{1..4}
mdadm: /dev/sdd1 appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Mar 7 17:25:51 2023
mdadm: /dev/sdd2 appears to be part of a raid array:
level=raid5 devices=3 ctime=Tue Mar 7 17:25:51 2023
mdadm: largest drive (/dev/sdd4) exceeds size (2094080K) by more than 1%
Continue creating array? yes
mdadm: Fail create md7 when using /sys/module/md_mod/parameters/new_array
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md7 started.
└─cinder--volumes-cinder--volumes--pool 253:5 0 69G 0 lvm
sdd 8:48 0 10G 0 disk
├─sdd1 8:49 0 2G 0 part
│ └─md7 9:7 0 4G 0 raid5
├─sdd2 8:50 0 2G 0 part
│ └─md7 9:7 0 4G 0 raid5
├─sdd3 8:51 0 2G 0 part
│ └─md7 9:7 0 4G 0 raid5
└─sdd4 8:52 0 4G 0 part
└─md7 9:7 0 4G 0 raid5
sde 8:64 0 10G 0 disk
[root@compute ~]# mdadm -D /dev/md7 /dev/md7: Version : 1.2 Creation Time : Wed Mar 8 14:52:00 2023 Raid Level : raid5 Array Size : 4188160 (3.99 GiB 4.29 GB) Used Dev Size : 2094080 (2045.00 MiB 2144.34 MB) Raid Devices : 3 Total Devices : 4 Persistence : Superblock is persistent Update Time : Wed Mar 8 14:52:11 2023 State : clean Active Devices : 3 Working Devices : 4 Failed Devices : 0 Spare Devices : 1 Layout : left-symmetric Chunk Size : 512K Consistency Policy : resync Name : compute:7 (local to host compute) UUID: 700d9a77:0babc26d:3b5a6768:223d47a8 Events : 18 Number Major Minor RaidDevice State 0 8 49 0 active sync /dev/sdd1 1 8 50 1 active sync /dev/sdd2 4 8 51 2 active sync /dev/sdd3 3 8 52 - spare /dev/sdd4
[root@compute ~]# mdadm /dev/md7 -f /dev/sdd1 mdadm: set /dev/sdd1 faulty in /dev/md7 [root@compute ~]# mdadm -D /dev/md7 /dev/md7: Version : 1.2 Creation Time : Wed Mar 8 14:52:00 2023 Raid Level : raid5 Array Size : 4188160 (3.99 GiB 4.29 GB) Used Dev Size : 2094080 (2045.00 MiB 2144.34 MB) Raid Devices : 3 Total Devices : 4 Persistence : Superblock is persistent Update Time : Wed Mar 8 14:59:00 2023 State : clean, degraded, recovering Active Devices : 2 Working Devices : 3 Failed Devices : 1 Spare Devices : 1 Layout : left-symmetric Chunk Size : 512K Consistency Policy : resync Rebuild Status : 66% complete Name : compute:7 (local to host compute) UUID: 700d9a77:0babc26d:3b5a6768:223d47a8 Events : 30 Number Major Minor RaidDevice State 3 8 52 0 spare rebuilding /dev/sdd4 1 8 50 1 active sync /dev/sdd2 4 8 51 2 active sync /dev/sdd3 0 8 49 - faulty /dev/sdd1
[root@compute ~]# mdadm /dev/md7 -r /dev/sdd1 mdadm: hot removed /dev/sdd1 from /dev/md7 [root@compute ~]# mdadm -D /dev/md7 /dev/md7: Version : 1.2 Creation Time : Wed Mar 8 14:52:00 2023 Raid Level : raid5 Array Size : 4188160 (3.99 GiB 4.29 GB) Used Dev Size : 2094080 (2045.00 MiB 2144.34 MB) Raid Devices : 3 Total Devices : 3 Persistence : Superblock is persistent Update Time : Wed Mar 8 15:00:22 2023 State : clean Active Devices : 3 Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Layout : left-symmetric Chunk Size : 512K Consistency Policy : resync Name : compute:7 (local to host compute) UUID: 700d9a77:0babc26d:3b5a6768:223d47a8 Events : 38 Number Major Minor RaidDevice State 3 8 52 0 active sync /dev/sdd4 1 8 50 1 active sync /dev/sdd2 4 8 51 2 active sync /dev/sdd3
[root@compute ~]# mdadm /dev/md7 -a /dev/sdd1 mdadm: added /dev/sdd1 [root@compute ~]# mdadm -D /dev/md7 /dev/md7: Version : 1.2 Creation Time : Wed Mar 8 14:52:00 2023 Raid Level : raid5 Array Size : 4188160 (3.99 GiB 4.29 GB) Used Dev Size : 2094080 (2045.00 MiB 2144.34 MB) Raid Devices : 3 Total Devices : 4 Persistence : Superblock is persistent Update Time : Wed Mar 8 15:01:29 2023 State : clean Active Devices : 3 Working Devices : 4 Failed Devices : 0 Spare Devices : 1 Layout : left-symmetric Chunk Size : 512K Consistency Policy : resync Name : compute:7 (local to host compute) UUID: 700d9a77:0babc26d:3b5a6768:223d47a8 Events : 39 Number Major Minor RaidDevice State 3 8 52 0 active sync /dev/sdd4 1 8 50 1 active sync /dev/sdd2 4 8 51 2 active sync /dev/sdd3 5 8 49 - spare /dev/sdd1