Dell PowerEdge RAID Controller H700 - Manual (Page 17)

Overview 17
RAID Description
RAID is a group of independent physical disks that provides high performance
by increasing the number of disks used for saving and accessing data.
A RAID disk subsystem offers the following benefits:
• Improves I/O performance and data availability.
• Improves data throughput because several disks are accessed
simultaneously. The physical disk group appears either as a single storage
unit or multiple logical units to the host system.
• Improves 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.
CAUTION: 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 and 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 is 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.
PERC7.2_UG.book Page 17 Thursday, March 3, 2011 2:14 PM