Patrol Read - Dell PowerEdge H730P User Manual

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
disk. The physical disk with the SMART error is marked as failed only after the successful completion of
the Replace Member. This prevents the array from reaching degraded state.
If an automatic Replace Member occurs using a source disk that was originally a hot spare (that was used
in a rebuild), and a new disk added for the Replace Member operation as the target disk, the hot spare
reverts to the hot spare state after a successful Replace Member operation.
NOTE: To enable the automatic Replace Member, use the Dell OpenManage storage management
application. For information on manual Replace Member, see

Patrol Read

The Patrol Read feature is designed as a preventative measure to ensure physical disk health and data
integrity. Patrol Read scans and resolves potential problems on configured physical disks. The Dell
OpenManage storage management application can be used to start Patrol Read and change its behavior.
The following is an overview of Patrol Read behavior:
• 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 any disks involved in any of the following operations:
– Rebuild
– Replace Member
– Full or Background Initialization
– CC
– RLM or OCE
NOTE: By default, Patrol Read automatically runs every seven days on configured SAS and SATA
hard drives. Patrol Read is not necessary on SSD and is disabled by default.
For more information on Patrol Read, see the Dell OpenManage documentation at dell.com/support/
manuals.
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Replacing An Online Physical Disks.