Planet NAS-5400, User Manual

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RAID 0 (striping)
In a RAID 0 array, data is split and stored in different locations, but without fault tolerance. The
server treats the array as one big disk, with a size of almost all individual disks combined. The
parallel access to multiple disks allows for faster read and write, making the array faster than
individual disks. Because of that, this configuration is ideal for applications where large amounts
of streaming data have to be efficiently transferred while assuring good quality, e.g. in a recording.
RAID 0 offers no mirroring or redundancy options. If one disk in the array fails, the entire array is
inoperable. RAID 0 is not fault-tolerant.
RAID 1 (mirroring)
A RAID 1 array consists of at least two disks that duplicate the storage of data; data is always
written to all disks. This system is rather fault-tolerance and is often used in environments with
multiple users where safety is of great importance, but more expensive than other solutions, since
the actual storage capacity is only 1 disk. RAID 1 is often used in environments with multiple users
where safety is of great importance.
RAID 5
RAID 5 is the same as RAID 0, i.e. using multiple disks to emulate one large virtual disk, but using
parity data format to store redundant information. While the user is writing data, RAID 5 scans the
data and stores redundancy information on a separate disk in the array. Parity information is split
and stored on different disks together with the actual data. If one disk in the array fails, parity data
on the safeguard disk can still be used to rebuild the entire information.
In other words, in a RAID 5 array, you use one disk for redundancy data, leaving you with n-1
disks available for actual data storage.
RAID 5 with Spare
RAID 5 with Spare is a RAID 5 configuration with one additional spare disk. Should any disk in the
array break down, the spare disk will automatically go online and rebuild damaged data. In other
words, you are providing two disks for safety, leaving you with n-2 disks storage capacity in an
array of n disks.
Note: Even though RAID greatly increases the level of safety in your system, you should still
make it a habit to back up data periodically. If you accidentally erase data, even a RAID array
cannot restore it. RAID can only compensate for the failure of one disk, that is, if two disks fail
simultaneously, data loss is inevitable.