Areca ARC-1880 Series User Manual page 182

APPENDIX
on the existing volume sets (residing on the newly expanded
RAID set) is redistributed evenly across all the disks. A contigu-
ous block of unused capacity is made available on the RAID set.
The unused capacity can be used to create additional volume
sets.
A disk, to be added to a RAID set, must be in normal mode (not
failed), free (not spare, in a RAID set, or passed through to
host) and must have at least the same capacity as the smallest
disk capacity already in the RAID set.
Capacity expansion is only permitted to proceed if all volumes
on the RAID set are in the normal status. During the expansion
process, the volume sets being expanded can be accessed by
the host system. In addition, the volume sets with RAID level 1,
10, 3, 5 or 6 are protected against data loss in the event of disk
failure(s). In the case of disk failure, the volume set changes
from "migrating" state to "migrating+degraded" state. When the
expansion is completed, the volume set would then transition to
"degraded" mode. If a global hot spare is present, then it further
changes to the "rebuilding" state.
The expansion process is illustrated as following figure.
RAID controller redistributes the original volume set over the
original and newly added disks, using the same fault-tolerance
configuration. The unused capacity on the expand RAID set can
then be used to create an additional volume set, with a different
fault tolerance setting (if required by the user.)
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