Users Guide

Source RAID Level Target RAID Level Number of Physical

Disks (Beginning)

Number of Physical

Disks (End)

Capacity Expansion

Possible

Description

reclaims disk space

used for it.

RAID 6 RAID 6 4 or more 5 or more Yes Increases capacity by

adding disks

RAID 10 RAID 10 Less than 32 32 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 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 specications, see t10.org and for detailed information on SATA interface

specications, 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 rst SMART error occurs on a physical disk that is part of a virtual disk. The target disk

needs to be a hot spare that qualies 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.

Features