The Problem
On CentOS/RHEL 6, a disk has issue and mdadm command shows /dev/md5 was active, degraded state .
# mdadm -Q --detail /dev/md5 /dev/md5: Version : 0.90 Creation Time : Wed Apr 12 09:50:21 2017 Raid Level : raid1 Array Size : 10485696 (10.00 GiB 10.74 GB) Used Dev Size : 10485696 (10.00 GiB 10.74 GB) Raid Devices : 2 Total Devices : 1 Preferred Minor : 5 Persistence : Superblock is persistent Update Time : Mon Jun 5 14:47:09 2017 State : active, degraded Active Devices : 1 Working Devices : 1 Failed Devices : 0 Spare Devices : 0 UUID : bdd69b24:0502f47d:04894333:532a878b Events : 0.358889 Number Major Minor RaidDevice State 0 0 0 0 removed 1 8 21 1 active sync /dev/sdb5
The Solution
The degraded state will generally occur if actual physical drive is going down, a drive temporarily being not communicating properly Or synchronization haven’t worked after the replacement of the disk.
If the drive is still online then there is a ‘Rebuild’ or ‘Synchronize’ option still be available. If so, then it will scan the drive that the system presumes is correct, and make sure ALL of the data is copied to the other drive.
Engage the hardware vendor and verify why the synchronize or rebuild function didn’t work during the replacement of RAID.
-- After the replacement -- [root@localhost ~]# mdadm -Q --detail /dev/md5 /dev/md5: Version : 0.90 Creation Time : Wed Apr 12 09:50:21 2017 Raid Level : raid1 Array Size : 10485696 (10.00 GiB 10.74 GB) Used Dev Size : 10485696 (10.00 GiB 10.74 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 5 Persistence : Superblock is persistent Update Time : Mon Jun 12 17:34:10 2017 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 UUID : bdd69b24:0502f47d:04894333:532a878b Events : 0.818295 Number Major Minor RaidDevice State 0 8 213 0 active sync /dev/sdn5 1 8 21 1 active sync /dev/sdb5