4big Quadra USB 3.0 User Manual
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RAID 5: In RAID 5, data is striped across all disks (minimum of three) and a parity block for each data block (P
in the illustration below) is written on the same stripe. If one physical disk fails, the data from the failed disk can
be rebuilt onto a replacement disk. No data is lost in the case of a single disk failure, but if a second disk fails
before data can be rebuilt to a replacement drive, all data in the array will be lost.
RAID 5+Spare: RAID 5+Spare is a RAID 5 array in which one disk is used as spare to rebuild the system as
soon as a disk fails. At least four disks are required. If one physical disk fails, the data remains available because
it is read from the parity blocks. Data from a failed disk is rebuilt onto the hot spare disk. When a failed disk is
replaced, the replacement becomes the new hot spare. No data is lost in the case of a single disk failure, but if a
second disk fails before the system can rebuild data to the hot spare, all data in the array will be lost.