Users Guide

Source RAID

Level

Target RAID

Level

Number of

Physical Disks

(Beginning)

Number of

Physical Disks

(End)

Capacity

Expansion

Possible

Description

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 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

• 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

disk. The physical disk with the SMART error is marked as failed only after the successful completion of

the Replace Member. This avoids putting the array in degraded status.