I've had to (temporary) reduce my RAID5-Array, so that there are four out of five disks available. Things getting worse as my system crashed during write process. After reboot the system wants to start "Background Reconstruction" as it normally does to an intact array to reconstruct the missing redundancy. As the array is degraded, this reconstruction does not start (see https://raid.wiki.kernel.org/index.php/Tweaking,_tuning_and_troubleshooting#Autodetection last paragraph on what the Reconstruction does).
I want to make my array active again but a mdadm --run /dev/md127 produces an input/output error (same "background reconstruction"-message under syslog). I know that I am loosing some MB of data- but how can I get my array back to work?
/dev/md127:
Version : 1.2
Raid Level : raid5
Used Dev Size : 1360148480 (1297.14 GiB 1392.79 GB)
Raid Devices : 5
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Fri Jun 14 10:54:22 2013
State : active, degraded, Not Started
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 512K
Name : mars:RA
UUID : 05c6d9f1:87571dc6:ee0d9f6b:c0b0c320
Events : 159201
Number Major Minor RaidDevice State
7 8 18 0 active sync /dev/sdb2
8 8 66 1 active sync /dev/sde2
2 0 0 2 removed
5 8 34 3 active sync /dev/sdc2
9 8 50 4 active sync /dev/sdd2