Disk space usage in RAID

RAID, short for a Redundant Array of Inexpensive Disks, is a method of combining several disks to a single logical storage unit. There are many possible ways to build a RAID, called RAID levels.

Certain RAID levels, most notably RAID 5 and RAID 1, provide a fault tolerance by storing certain amount of redundant data. This way, if a single drive fails, the array does not lose the data and can still provide read and write access, albeit at a cost of a performance loss.

For RAID 1, the half of the array capacity is used to hold redundant data and is not available for use. For RAID 5, the equivalent capacity of one of the array disks is not available for use.

For more complex estimations of the capacity, fault tolerance, and other side effects, use the online RAID Calculator.

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