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INTRODUCTION
17
mation or data on that RAID set. Therefore, if a server fails, the
RAID set disk drives can be moved to another server with an
Areca RAID controller and the disks can be inserted in any order.
1.3.3.3 Online Capacity Expansion
Online Capacity Expansion makes it possible to add one or more
physical drives to a volume set without interrupting server op-
eration, eliminating the need to backup and restore after recon-
guration of the RAID set. When disks are added to a RAID set,
unused capacity is added to the end of the RAID set. Then, data
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,
1E, 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 transitions
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
transitions to the “rebuilding” state.