Hitachi Compute Rack CR 210H User Manual page 28

RAID6
Parity 1
Block 4
Disk 1
Figure 3-4: RAID6 method
Data is striped block by block on all the HDDs together with array parity.
Advantage:

– As compared to RAID5, two types of parities generated improve
redundancy.
– Data distribution onto HDDs provides data redundancy. Therefore, a read
or write can be performed on each HDD independently. Data striping on a
block basis is suitable for transaction processing.
– Even if up to two of the HDDs in the disk array fail, read or write
processing can be continued while array parity is computing the lost data.
HDD interchange enables data reconstruction without shutting down
operations.
– The array parity distributed on each HDD has the advantage that parallel
processing by independent access to HDDs is implemented during data
write operation.
Disadvantage:

– RAID6 is inferior to RAID5 in write performance because of two types of
parities generated during write processing.
– An attempt to read or write data during data rebuild causes a decrease
in processing performance.
Number of HDDs required: 4 (min.) to 6 (max.)

3-6
Host
Array Controller
Parity 2 Block 1
Parity 1 Parity 2
Disk 2 Disk 3
System Unit Functions
Hitachi Compute Rack 210H User's Guide
Data
Block 2 Block 3
Block 5 Block 6
Disk 4 Disk 5