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Chapter 3. RAID Functions and Array States
This chapter describes the RAID functions and the states of RAID arrays.
RAID Functions
Redundant Array of Independent Disks (RAID) technology provides:
v Larger disk size
v Immediate availability and recovery of data
v Redundancy of data at a level that you can choose.
RAID technology stores data across groups of disk drives that are known as arrays.
These arrays are contained in array subsystems, which can be configured with one or
more arrays. All arrays, except RAID-0 arrays, can provide data redundancy that
ensures that no data is lost if one disk drive in the array fails.
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An Advanced SerialRAID Adapter, which uses microcode below level 5000, provides
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RAID-0 and RAID-5 functions to control the arrays of the RAID subsystem. An
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Advanced SerialRAID Plus Adapter, which uses microcode at or above level 5000,
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provides RAID-0, RAID-1, RAID-5, and RAID-10 functions.
The main characteristics of the various RAID types are as follows:
v RAID-0 provides data striping across disk drives, but provides no added protection
against loss of data.
v RAID-1 provides data mirroring across two member disk drives to protect against
loss of data.
v RAID-5 provides data striping with parity data across disk drives to provide protection
against loss of data.
v RAID-10 provides data striping and data mirroring across disk drives to provide
protection against loss of data.
Availability
Availability is an important consideration that can affect the way you configure your
arrays. It is the ability of a system to continue operating, although one or more of its
components have failed.
v RAID-0 provides data availability equivalent to that of a standard disk drive, but with
better performance for long data transfer operations.
v RAID-1 provides good data availability because data is mirrored on two member disk
drives, as it is with RAID-10. RAID-1 arrays, however, have only two member disk
drives. Member disk drives of a RAID-1 array can be configured to be in separate
domains. Separate domains ensure that data remains available if, for example, a
complete domain fails through loss of power.
v RAID-5 provides good data availability with good performance for workloads that
include many read and write operations.
v RAID-10 provides good data availability and performance that is better than that
provided by RAID-5, especially when a member disk drive has failed. For long data
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