A hard drive was thrown out of my raid 5 array and had to be readded.
The command gave the following error message:
mdadm: An option must be given to set the mode before a second device
Solution to get it working:
In my case the name of the raid device is md0 (which contains disk sdb, sdc and sdd. For the linux system i use sda).
Now i wanted to add the first partition of my sdb hard drive again to the raid array.
root@homeserver:/home/mathias# mdadm /dev/md0 -a /dev/sdb1 mdadm: re-added /dev/sdb1 And now the raid array is syncing again :) root@homeserver:/home/mathias# cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10] md0 : active raid5 sdb1 sdc1 sdd1 5860259840 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/2] [_UU] [>....................] recovery = 0.8% (24866428/2930129920) finish=262.8min speed=184190K/sec bitmap: 11/22 pages [44KB], 65536KB chunk unused devices: <none>
Further information: How to create a crypted raid5