Growing

Adding partitions

When new disc is added, existing raid partitions can be grown to use the new disc. After the new disc was partitioned, the RAID level 1/4/5/6 array can be grown for example using this command (assuming that before growing it contains three drives):

mdadm --add /dev/md1 /dev/sdb3
mdadm --grow --raid-devices=4 /dev/md1

The process can take even 10 hours. There is a critical section at start, which cannot be backed up. To allow recovery after unexpected power failure, an additional option --backup-file= can be specified.

Expanding existing partitions

It is possible to move whole RAID array to bigger disc drives by replacing one by one. In the end the number of devices will be the same, but the underlying partitions on which RAID resides will be bigger. It is possible to --grow RAID arrays so they will expand to utilize whole available space.

This section, about how to do it, needs to be written by someone who did this.