The MD plug-in allows the child objects of a RAID region to be replaced with other available objects. This is accomplished using the general EVMS replace function. Please see Chapter 22, Replacing objects for more detailed information about how to perform this function.
For all RAID levels, the replacement object must be at least as big as the child object being replaced. If the replacement object is bigger than the child object being replaced, the extra space on the replacement object will be unused. In order to perform a replace operation, any volumes that comprise the RAID region must be unmounted.
This capability is most useful for Linear-RAID and RAID-0 regions. It is also allowed with RAID-1 and RAID-4/5, but those two RAID levels offer the ability to mark objects faulty, which accomplishes the same end result. Because that process can be done while the region is in use, it is generally preferable to object-replace, which must be done with the region deactivated.