Hello, I've a system with a RAID1 using two disks (sda + sdb) + 1 spare (sdc). For some stupid reason (cable) the spare (sdc) became active and sda was out the array. I then added back sda to the RAID1 but now I've RAID1 with three active disks and zero spare. I don't understand why the spare device didn't switch back as spare after sda have been rebuild. I used the following command to add sda to the RAID1: # mdadm /dev/md0 --add /dev/sda3 What did I do wrong here? And how to fix it? Do I have to set sdc to faulty and add it back? Thanks! Here are the RAID1 status: # cat /proc/mdstat Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10] md0 : active raid1 sda3[2] sdc3[3](W)(R) sdb3[0] 976015360 blocks super 1.2 [2/3] [UU] bitmap: 1/8 pages [4KB], 65536KB chunk # mdadm --detail /dev/md0 /dev/md0: Version : 1.2 Creation Time : Wed Sep 5 09:45:55 2018 Raid Level : raid1 Array Size : 976015360 (930.80 GiB 999.44 GB) Used Dev Size : 976015360 (930.80 GiB 999.44 GB) Raid Devices : 2 Total Devices : 3 Persistence : Superblock is persistent Intent Bitmap : Internal Update Time : Sun Feb 23 18:28:45 2020 State : clean Active Devices : 3 Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Consistency Policy : bitmap Name : sharon:2 UUID : 98299cb7:9cbe61e9:c8374bcb:3c72d5ca Events : 704774 Number Major Minor RaidDevice State 0 8 19 0 active sync /dev/sdb3 2 8 3 1 active sync /dev/sda3 3 8 35 1 active sync writemostly /dev/sdc3 -- Aymeric
