Dell PowerEdge RAID Controller 6i - Manual (Page 17)

Overview
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RAID Description
RAID is a group of independent physical disks that provides high performance by
increasing the number of drives used for saving and accessing data. A RAID disk
subsystem improves I/O performance and data availability. The physical disk
group appears to the host system either as a single storage unit or multiple logical
units. Data throughput improves because several disks are accessed
simultaneously. RAID systems also improve data storage availability and fault
tolerance. Data loss caused by a physical disk failure can be recovered by rebuilding
missing data from the remaining physical disks containing data or parity.
NOTICE:
In the event of a physical disk failure, a RAID 0 virtual disk fails, resulting in
data loss.
Summary of RAID Levels
RAID 0 uses disk striping to provide high data throughput, especially for large
files in an environment that requires no data redundancy.
RAID 1 uses disk mirroring so that data written to one physical disk is
simultaneously written to another physical disk. RAID 1 is good for small
databases or other applications that require small capacity, but also require
complete data redundancy.
RAID 5 uses disk striping and parity data across all physical disks (distributed
parity) to provide high data throughput and data redundancy, especially for
small random access.
RAID 6 is an extension of RAID 5 and uses an additional parity block. RAID 6
uses block-level striping with two parity blocks distributed across all member
disks. RAID 6 provides protection against double disk failures and failures
while a single disk is rebuilding. If you are using only one array, deploying
RAID 6 is more effective than deploying a hot spare disk.
RAID 10, a combination of RAID 0 and RAID 1, uses disk striping across
mirrored disks. It provides high data throughput and complete data redundancy.
RAID 10 can support up to eight spans, and up to 32 physical disks per span.
RAID 50, a combination of RAID 0 and RAID 5, uses distributed data parity
and disk striping and works best with data that requires high system availability,
high request rates, high data transfers, and medium-to-large capacity.
RAID 60 is a combination of RAID 6 and RAID 0, a RAID 0 array is striped
across RAID 6 elements. RAID 60 requires at least 8 disks.
Dell_PERC6.1_UG.book Page 17 Wednesday, April 15, 2009 4:18 PM