B.3.1. Expanding and shrinking MD arrays (linear and RAID-1)
If the MD region is part of a compatibility volume and the MD region is
the topmost object of the volume, it's possible to expand and shrink the MD region.
B.3.1.1. Expanding a linear MD region
A linear MD region can be expanded either by expanding the last member
or by adding a new member.
B.3.1.2. Shrinking a linear MD region
A linear MD region can be shrunk either by shrinking the last member
or by removing disks from the array (last member first).
B.3.1.3. Expanding a RAID-1 MD region
A RAID-1 MD region can only be expanded if all members can be expanded.
B.3.1.4. Shrinking a RAID-1 MD region
A RAID-1 MD region can only be shrunk if all members can be shrunk.
B.3.2. Adding an active object (RAID-1 only)
Use this option to increase the number of mirrors of the RAID-1 region, from
n-way mirrors to (n+1)-way mirrors. When the operation is committed, the
kernel MD driver performs a resync of the MD array.