Summary
A rebuild of a mdadm disk array can be performed automatically.
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To put a faulty disk back into the array, it must first be removed using the command mdadm --manage /dev/mdN -r /dev/sdX1 and then added again with mdadm --manage /dev/mdN -a /dev/sdd1.
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When restoring the complete RAID, including the second hard disk, the data must be synchronized.
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According to
Summary
A rebuild is performed automatically. The disk set to faulty appears in the output of mdadm -D /dev/mdN as faulty spare .
To put it back into the array as a spare disk, it must first be removed using mdadm --manage /dev/mdN -r /dev/sdX1 and then added again mdadm --manage /dev/mdN -a /dev/sdd1 .
Mdadm recovery and resync - Thomas-Krenn-Wiki
thomas-krenn.com
Summary
This example illustrates how Linux Software RAID behaves during continued operation on a degraded array. A partition is deleted, the array is installed and the data is written, and then the previously removed partition is added. When restoring the complete RAID, including the second hard disk, this data must be synchronized.
Mdadm recover degraded Array procedure - Thomas-Krenn-Wiki
thomas-krenn.com
This duly told us what it found on the disks, and asked for confirmation. Please make sure you've preserved that mdadm --examine output before you give that ...
RAID Recovery - Linux Raid Wiki
kernel.org
This happens because if there is no RAID configuration information in the mdadm.conf file, the system may create a RAID device from one disk in the array, ...
RAID setup - Linux Raid Wiki
kernel.org
