Dell UCPB-900, UCSE-900, UCSA-901, UCPA-901, UCSB-900, and UCPE-900 Fault tolerance, Smart Feature

Source RAID	Target RAID	Number of	Number of	Capacity	Description
Level	Level	Physical Disks	Physical Disks	Expansion
		(Beginning)	(End)	Possible
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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