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• Support for controller failover in systems with Fault Tolerant Shared PERC 8 card configuration.
The following 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.
Patrol Read
The Patrol Read feature is designed as a preventive measure to ensure physical disk health and data
integrity. Patrol Read scans for and resolves potential problems on configured physical disks. The Dell
Chassis Management Controller (CMC) can be used to start and control the features of Patrol Read.
The following is an overview of Patrol Read:
• Patrol Read runs on all disks on the controller that are configured as part of a virtual disk, including
hot spares.
• Patrol Read does not run on physical disks that are not part of a virtual disk or are in Ready state.
• Patrol Read adjusts the amount of controller resources dedicated to Patrol Read operations based on
outstanding disk I/O. For example, if the system is busy processing I/O operation, then Patrol Read
uses fewer resources to allow the I/O to take a higher priority.
• Patrol Read does not run on disks involved in any of the following operations:
– Rebuild
– Replace Member
– Full or Background Initialization
– Consistency Check (CC)
NOTE: By default, Patrol Read automatically runs every seven days on configured SAS hard
drives. Patrol Read is not necessary on SSD and is disabled by default.
NOTE: In the event of a controller failover in systems with Fault Tolerant Shared PERC 8 card
configuration, Patrol Read does not continue on the active controller. You must start Patrol
Read again through CMC. If you do not start Patrol Read, it automatically starts on the active
controller within seven days of the failover.
For more information on Patrol Read, see the Dell Chassis Management Controller for PowerEdge VRTX
Online Help.
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