Raid 1 - Disk Mirroring/Disk Duplexing; Raid 5 - Data Striping With Striped Parity; Figure 39. Raid 1 - Disk Mirroring/Disk Duplexing - Intel SS4000-E - Entry Storage System NAS Server User Manual

Levels of RAID

RAID 1 - Disk Mirroring/Disk Duplexing

In a RAID 1 configuration, all the data written to one disk is duplicated on the other disk.
This offers greater data protection since if one disk fails, all your data is still intact on the
other disk. However, using RAID 1 means only half your available disk space is used for
data; the other half is used for a duplicate (mirror) of that data.
You can use RAID 1 only if your storage system has only two disks. If the disks are not
the same size, 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 fails, the other disk continues to make its data available.

RAID 5 - Data Striping with Striped Parity

Like RAID 0, RAID 5 offers increased performance by distributing the data across
multiple disks. But unlike RAID 0, RAID 5 also offers data protection. If your storage
system has three disks of equal size, two thirds of each disk are used for data, and the
remaining third contains the parity information needed to reconstruct either of the other
two. In this way, if any of the three disks fails, it can be reconstructed when a new disk is
installed in the storage system.
If your storage system has four disks of equal size, three fourths of each disk are used for
data, and the remaining fourth contains the parity information needed to reconstruct either
of the other three. If any of the four disks fails, it can be reconstructed when a new disk is
installed.
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, only 600 GB of
disk space would be available for data.
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Figure 39. RAID 1 - Disk Mirroring/Disk Duplexing

D1 D1
D2
D2
Disk 1 Disk 2
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Intel Entry Storage System SS4000-E User Guide