Dell PowerEdge RAID Controller S100 - Manual (Page 17)

Overview 17
About RAID
A RAID disk array 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 disks appear 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.
NOTE: When a physical disk in a RAID 0 virtual disk fails, data is lost because there
is no redundancy for this RAID level. However, when a physical disk in a
RAID 1, RAID 5, or RAID 10 fails, data is preserved because there is redundancy
with these RAID levels.
Summary of RAID Levels
• Volume uses available space on a single physical disk and forms a single
logical volume on which data is stored.
• 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
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.
• RAID 10 uses disk striping across two mirrored sets. It provides high data
throughput and complete data redundancy.
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