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Intel® Server RAID Controller U3-1 User’s Manual Rev 1.0 5-3
RAID Features
One or more physical disks may be added to an array to expand its capacity without rebooting.
When disks are added to an array, unused capacity is added to the end of the array. Data on RAID
volumes residing on that array is redistributed evenly across all the disks (including the new disks).
As a result, a contiguous block of unused capacity (disk space) is made available on the array. The
additional capacity created from adding disks can be used to create one or more RAID arrays and/
or new volumes.
A disk, to be added to an array, must be in normal mode (not failed), unused (not in an array, a
spare, or passed through to host) and must have at least the same capacity as the smallest disk
already in the array. Normally, all disks in an array should have the same capacity, since any
capacity on a disk beyond that of the smallest disk would be wasted.
Capacity expansion is only permitted to begin if all volumes on the array are in normal mode (not
degraded or failed) and a idle state (not rebuilding, initializing, transforming etc.). During the
expansion process, the RAID volumes being expanded are accessible by the system. In addition,
RAID volumes with RAID levels 1 or 5 are protected against data loss in the event of a single disk
failure. In the case of a single disk failure, the RAID volume transitions from normal mode,
expanding state to degraded mode, expanding state. When the expansion is completed, the volume
transitions to degraded mode, idle state. If a global hot spare is present, then it further transitions to
degraded mode, rebuilding state. After the rebuild is complete, the volume transitions from
rebuilding state to idle state, normal mode.
To begin an expansion, an array must be in an idle state (not already expanding).
The result of array expansion is illustrated in Figure 5-1.
Figure 5-1. Array Expansion
Array_0 6000 Mb
Disk 0
2000 Mb
Disk 1
2000 Mb
Disk 2
2000 Mb
Free Space - 1800 Mb
Volume 1 - 2400 Mb
Volume 0 - 1800 Mb
Before Array Expansion
Array_0 8000 Mb
Disk 0
2000 Mb
Disk 1
2000 Mb
Disk 2
2000 Mb
Disk 3
2000 Mb
Free Space - 3800 Mb
Volume 1 - 2400 Mb
Volume 0 - 1800 Mb
After Array Expansion (By Adding One Disk)