Source RAID
Level Target RAID
Level Number of
Physical Disks
(Beginning)
Number of
Physical Disks
(End)
Capacity
Expansion
Possible
Description
RAID 6 RAID 5 4 or more 4 or more Yes Removes one
set of parity
data and
reclaims disk
space used for
it.
RAID 6 RAID 6 4 or more 5 or more Yes Increases
capacity by
adding disks
NOTE: The total number of physical disks in a disk group cannot exceed 32. You cannot perform
RAID level migration and expansion on RAID levels 10, 50, and 60.
Fault tolerance
The PERC 9 series supports the following:
• Self Monitoring and Reporting Technology (SMART)
• Patrol Read
• Physical disk failure detection
• Physical disk rebuild using hot spares
• Controller cache preservation
• Battery and non-volatile cache backup of controller cache to protect data
• Detection of batteries with low charge after boot up
The next sections describe some methods to achieve fault tolerance.

The SMART Feature

The SMART feature monitors certain physical aspects of all motors, heads, and physical disk electronics
to help detect predictable physical disk failures. Data on SMART-compliant physical disks can be
monitored to identify changes in values and determine whether the values are within threshold limits.
Many mechanical and electrical failures display some degradation in performance before failure.
A SMART failure is also referred to as predicted failure. There are numerous factors that are predicted
physical disk failures, such as a bearing failure, a broken read/write head, and changes in spin-up rate. In
addition, there are factors related to read/write surface failure, such as seek error rate and excessive bad
sectors.
NOTE: For detailed information on SCSI interface specifications, see t10.org and for detailed
information on SATA interface specifications, see t13.org.

Automatic replace member with predicted failure

A Replace Member operation can occur when there is a SMART predictive failure reporting on a physical
disk in a virtual disk. The automatic Replace Member is initiated when the first SMART error occurs on a
physical disk that is part of a virtual disk. The target disk needs to be a hot spare that qualifies as a rebuild
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