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You can use RAID 5 only if your storage system has at least three disks. If the disks are
not the same size, the smallest of the disks determines how much disk space is available
for data. For example, if one disk is 300 GB, one is 400 GB, and one is 500 GB, only 300
GB from each disk can be used. Two thirds of each disk (200 GB) is used for storage
space, and the remaining third is used for parity information. As a result, for all three disks,
only 600 GB of disk space would be available for data.
• RAID 5 + spare: In this configuration, three of the disks use RAID 5, and the fourth is
empty. If any of the three disks fails, it is immediately rebuilt using the fourth spare disk. As
a result, you can remove the failed disk and still have the ongoing fast performance and
data protection offered by RAID 5. When the failed disk is repaired or replaced and
re-installed into the storage system, it automatically becomes the spare for the other
functioning three.
You can use RAID 5 + spare only if your storage system has four disks. If the disks are not
the same size, the smallest of the disks determines how much disk space is available for
data, similar to RAID 5.
• RAID 10: RAID 10 is similar to RAID 1, but rather than having one disk mirror to one other
disk, two disks mirror to the two other disks.
You can use RAID 10 only if your storage system has four disks. The disks in the first two
slots constitute the first pair, and the disks in the second two slots constitute the second
pair. In each pair, the smaller of the two disks is used for data, and the larger of the two
disks is used as the mirror.
If one disk in the pair fails, the other disk continues to make its data available.
A.1 Adding Hard Disks
The effect of adding hard disks to your storage system varies, depending on the disk
configuration you chose when you configured the system and the current state of the existing
disks.
For example, in a linear configuration, you can add a new disk at any time, and data can be
written to that disk as soon as it is added. Whether you previously removed a disk or one of the
other disks failed makes no difference.
In a RAID configuration, the effect of adding a disk varies, depending on whether the RAID is
in a normal or degraded state (as indicated on the Disks page). A normal state indicates that
the RAID is functioning properly. A degraded state indicates that one or more disks have been
removed or failed, but because of the data protection offered by the RAID, you can continue to