Users guide

17 Intel® RAID Software User Guide
Table 8. RAID 60 Overview
The following figure shows a RAID 6 data layo
ut. The second set of parity drives are
denoted by Q. The P drives follow the RAID 5 parity scheme.
Note: When only thr
ee hard drives are available for RAID 6, the situation has to be that P
equals Q equals original data, which means that the three hard drives have the same
original data, which can afford two disk failures.
Uses
Provides a high level of data protection through the use of a second parity
block in each stripe. Use RAID 60 for data that requires a very high level of
protection from loss.
In the case of a failure of one drive or two drives in a RAID set in a virtual
disk, the RAID controller uses the parity blocks to recreate all the missing
information. If two drives in a RAID 6 set in a RAID 60 virtual disk fail, two
drive rebuilds are required, one for each drive. These rebuilds do not occur at
the same time. The controller rebuilds one failed drive, and then the other
failed drive.
Use for office automation, online customer se
rvice that requires fault
tolerance or for any application that has high read request rates but low write
request rates.
Strong Points
Provides data redundancy, high read rates, an
d good performance in most
environments. Each RAID 6 set can survive the loss of two drives or the loss
of a drive while another drive is being rebuilt. Provides the highest level of
protection against drive failures of all of the RAID levels. Read performance
is similar to that of RAID 50, though random reads in RAID 60 might be
slightly faster because data is spread across at least one more disk in each
RAID 6 set.
Weak Points
Not well suited to tasks requiring a lot of writes. A RAID 60 virtual disk has to
generate two sets of parity data for each write operation, which results in a
significant decrease in performance during writes. Disk drive performance is
reduced during a drive rebuild. Environments with few processes do not
perform as well because the RAID overhead is not offset by the performance
gains in handling simultaneous processes. RAID 6 costs more because of
the extra capacity required by using two parity blocks per stripe.
Drives
A minimum of 6.