Dell PERC 4/SI - Manual (Page 16)

Logical Drive States
The logical drive states are described in Table 2 -4 .
Table 2-4. Logical Drive States
Enclosure Management
Enclosure management is the intelligent monitoring of the disk subsystem by software and/or hardware. The disk subsystem can be part of the host computer
or can reside in an external disk enclosure. Enclosure management helps you stay informed of events in the disk subsystem, such as a drive or power supply
failure. Enclosure management increases the fault tolerance of the disk subsystem.
RAID Levels
The RAID controller supports RAID levels 0, 1, 5, 10, and 50. The supported RAID levels are summarized in the following section. In addition, it supports
independent drives (configured as RAID 0.) The following sections describe the RAID levels in detail.
Summary of RAID Levels
RAID 0 uses striping to provide high data throughput, especially for large files in an environment that does not require fault tolerance.
RAID 1 uses mirroring so that data written to one disk drive is simultaneously written to another disk drive. This is good for small databases or other
applications that require small capacity, but complete data redundancy.
RAID 5 uses disk striping and parity data across all drives (distributed parity) to provide high data throughput, especially for small random access.
RAID 10, a combination of RAID 0 and RAID 1, consists of striped data across mirrored spans. It provides high data throughput and complete data redundancy,
but uses a larger number of spans.
RAID 50, a combination of RAID 0 and RAID 5, uses distributed parity and disk striping and works best with data that requires high reliability, high request
rates, high data transfers, and medium-to-large capacity.
Selecting a RAID Level
To ensure the best performance, you should select the optimal RAID level when you create a system drive. The optimal RAID level for your disk array depends
on a number of factors:
Hot Spare The physical drive is powered up and ready for use as a spare in case an online drive fails.
Fail A fault has occurred in the physical drive, placing it out of service.
Rebuild The physical drive is being rebuilt with data from a failed drive.
State Description
Optimal The logical drive operating condition is good. All configured physical drives are online.
Degraded The logical drive operating condition is not optimal. One of the configured physical drives has failed or is offline.
Failed The logical drive has failed.
Offline The logical drive is not available to the RAID controller.
NOTE: Running RAID 0 and RAID 5 logical arrays on the same set of physical disks (a sliced configuration) is not recommended. In the event of a disk
failure, the RAID 0 logical drive will cause any rebuild attempt to fail.