Appendix 1 What Is Raid - Planet NAS-5400 User Manual

The acronym RAID stands for Redundant Array of Independent Drives, a method to combine a
number of small, inexpensive drives into an array which offers more functionality than a single
large disk with comparable capacity, while simultaneously taking advantage of the individual disks
to increase the efficiency of the system. In other words, during the writing process, data is split
into segments and stored on multiple disks; likewise, during the reading process, data is retrieved
simultaneously from multiple disks in order to increase the access speed of the array.
RAID can also be configured to use part of the disk capacity for mirroring or redundant data, thus
preserving the integrity of the system in case one of the disks in the array fails.
NAS-5400 supports RAID 0, RAID 1, RAID 5, and RAID 5 with Spare, described below:
RAID level
RAID 0
RAID 1
RAID 5
RAID 5 with Spare
Each of the RAID configurations offers a different disk capacity and level of safety. When making
your choice, consider the following:
1. The bigger the available space, the fewer safeguards the system has.
2. For any RAID array, the capacity of the array is determined by the smallest hard disk. E.g., for a
RAID 1 array created with one 20 GB and one 30 GB hard disks, the total available capacity is
defined based on the 20 GB hard disk. Therefore you should always choose to use hard disks
with identical size to create a RAID array.
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Functionality
Offers Striping, a process where multiple disks are combined
to form one virtual large disk, but without safety measures.
Half of the disks are used for backup purposes; the content of
disk A is mirrored to disk B to assure data integrity. The
available storage space is only one half of total physical disk
capacity.
This configuration includes a backup option. It treats multiple
disks as one virtual disk to increase access speed. It uses
parity mode to store redundant data on a space equal to the
size of one disk for later data recovery. The actual available
storage space in a system with n disks is thus n-1 hard disks.
RAID 5 with Spare adds one spare disk to the RAID 5 array,
allocating one for redundancy and the second one as a
spare. The actual available storage space in a system with n
disks is thus n-2 hard disks.
Appendix 1
What Is RAID