INTRODUCTION
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- figuration 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.
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