Freedom9 4020 - Manual (Page 97)

freeStor 4020 User’s Manual
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Appendix A: Disk Configurations
Your storage system supports the following types of disk configurations:
• Linear: A linear configuration is similar to using multiple hard disks in a regular computer.
Each disk is an independent entity, and the data on it is self-contained. You can add or
remove the disks without affecting the other disks. All the available disk space is used for
data.
If your storage system has only one disk, you must use a linear configuration. However, you
can use a linear configuration for two, three, or four disks as well.
• RAID 0: Instead of writing all the data to one disk in a linear fashion, some bytes are written
to one disk, and other bytes are written to another. Performance is faster because reading
and writing activities can occur on multiple disks simultaneously. All the available disk space
is used for data.
For RAID 0, your storage system must have at least two disks. However, you can use RAID
0 with three or four disks as well, and the disks can be any size.
• RAID 1: In this 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: 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, 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