d2, 2big, and 5big Network 2 User Manual 111
RAID5+Spare (5big only): 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.
RAID6 (5big only): In RAID 6, data is striped across all disks (minimum of four) and a two parity blocks for
each data block (p and q 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. This Raid mode can support up to two disk
failures with no data loss. RAID 6 provides for faster rebuilding of data from a failed disk.
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