Qsan XS5224D User Manual page 132

RAID 6 consists of block-level striping with double distributed parity. It requires a minimum
of four disks. Double parity provides fault tolerance up to two failed disk drives. This makes
larger RAID groups more practical, especially for high-availability systems, as large-capacity
drives take longer to restore. As with RAID 5, a single drive failure results in reduced
performance of the entire array until the failed drive has been replaced. With a RAID 6 array,
using drives from multiple sources and manufacturers, it is possible to mitigate most of the
problems associated with RAID 5. The larger the drive capacities and the larger the array
size, the more important it becomes to choose RAID 6 instead of RAID 5.
RAID 0+1 (RAID 1 on top of RAID 0)
RAID 0+1 creates a second striped set to mirror a primary striped set. The array continues to
operate with one or more drives failed in the same mirror set, but if drives fail on both sides
of the mirror, the data on the RAID system is lost.
RAID 10 (RAID 0 on top of RAID 1)
RAID 10 creates a striped set from a series of mirrored disk drives. The array can sustain
multiple drive losses so long as no mirror loses all its drives.
RAID 30 (RAID 3 on top of RAID 0)
RAID 30 is the combination of RAID 3 and RAID 0, do RAID 3 first, further RAID 0. It is
composed of multiple sets of RAID 3 stripe access to each other. Because RAID 30 is based
on RAID 3 which requires at least three disk drives, therefore RAID 30 is constituted a
plurality RAID 3, at least six disk drives. RAID 30 can still operate when appearing a
damaged disk drive in disk group of RAID 3. But if any one group of RAID 3 appears two or
two or more disk drives damaged, the entire RAID 30 will fail.
RAID 50 (RAID 5 on top of RAID 0)
RAID 50 is the combination of RAID 5 and RAID 0, do RAID 5 first, further RAID 0. The
concept is the same as RAID 30. RAID 50 requires at least six disk drives. Since RAID 50
constitutes stripe of multiple disk group of RAID 5, it has higher performance than RAID 5,
but capacity utilization is lower than RAID 5.
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