Areca 24/4 Internal/External Port Pcie 3.0 12 Gb/s SAS/SATA Raid Controller 2Gb Cache - Manual (Page 247)

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APPENDIX
set. Then, data on the existing volume sets (residing on the
newly expanded RAID set) is redistributed evenly across all
the disks. A contiguous 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 expan-
sion process, the volume sets being expanded can be ac-
cessed 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 vol-
ume set changes from “migrating” state to “migrating+de-
graded“ 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.)