Users Guide

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 oers the following benets:
• 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.
Topics:
• Summary of RAID levels
• RAID terminology
Summary of RAID levels
Following is the RAID levels supported by PERC 9 series of cards:
• RAID 0 uses disk striping to provide high data throughput, especially for large les 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 eective 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 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.
The following table lists the minimum and maximum disks supported on each RAID levels.
Table 15. Minimum and maximum disks supported on each RAID levels
RAID Level Minimum disk Maximum disk
0 1 32
1 2 2
5 3 32
6 4 32
10
112 Appendix RAID description