Appendix: 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.
CAUTION: In the event of a physical disk failure, a RAID 0 virtual disk fails, resulting in data loss.
A RAID disk subsystem offers the following benefits:
•
Improved I/O performance and data availability.
•
Improved 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.
•
Improved 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.
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.
•
RAID 50 is a combination of RAID 0 and RAID 5 where a RAID 0 array is striped across RAID 5 elements. RAID 50
requires at least six disks.
•
RAID 60 is a combination of RAID 0 and RAID 6 where a RAID 0 array is striped across RAID 6 elements. RAID 60
requires at least eight disks.
RAID Terminology
Disk Striping
Disk striping allows you to write data across multiple physical disks instead of just one physical disk. Disk striping
involves partitioning each physical disk storage space in stripes of the following sizes: 64 KB, 128 KB, 256 KB, 512 KB,
and 1024 KB. The stripes are interleaved in a repeated sequential manner. The part of the stripe on a single physical disk
is called a stripe element.
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