LaCie ICA-312 User Manual page 174

RAID 6
In RAID 6, data is striped across all disks (minimum of four) and two parity blocks for each data block (p and q in
the illustration below) are 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.
RAID 1+Spare(s), RAID 5+Spare(s), and RAID 6+Spare
RAID Mode Maximum Spare(s)
RAID 1
RAID 5
RAID 6
In a RAID 1 configuration, the same data is written across all hard disks in the array. With RAID 5 and RAID 6,
data is available from the parity blocks. In both cases, a RAID+Spare array gives you a "hot-spare" that is ready
to rebuild the system should a disk fail. If a hard disk in the RAID array fails, the data is immediately copied or
rebuilt onto the hot spare disk. The clear advantage for a RAID array with a spare is that you do not have to wait
for a replacement disk.
When the 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. It is possible to create an array with more than one spare.
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