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Features 27
Fault Tolerance
The list of features of the PERC cards that provide fault tolerance to prevent
data loss is as follows:
• Support for Self Monitoring and Reporting Technology (SMART)
• Support for Patrol Read
• Redundant path support (for PERC H810 only)
• Physical disk failure detection
• Physical disk rebuild using hot spares
• 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.
SMART-compliant physical disks have attributes for which data 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 a predicted failure. There are numerous
factors that relate to 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.