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RAID Levels
RAID Levels
The RAID level defines a storage architecture in which the storage capacity on the
drives in a volume group is separated into two parts: part of the capacity stores the
user data, and the remainder stores redundant or parity information about the user
data. The RAID level that you choose determines how user data is written to and
retrieved from the drives. Using the script commands, you can define five RAID
levels: RAID Level 0, RAID Level 1, RAID Level 3, RAID Level 5, and RAID Level
6. Each level provides different performance and protection features.
RAID Level 0 provides the fastest storage access but does not provide any redundant
information about the stored data. RAID Level 1, RAID Level 3, RAID Level 5, and
RAID Level 6 write redundancy information to the drives to provide fault tolerance.
The redundancy information might be a copy of the data or an error-correcting code
that is derived from the data. In RAID Level 1, RAID Level 3, RAID Level 5, or
RAID Level 6 configurations, if a drive fails, the redundancy information can be used
to reconstruct the lost data. Regardless of the RAID level that you choose, you can
configure only one RAID level across each volume group. All redundancy
information for a volume group is stored within the volume group. The following
table lists the RAID levels and describes the configuration capabilities of each level.
Disk pools are automatically configured to RAID Level 6 by the storage management
software. You cannot change the RAID level for disk pools.
Table 9 RAID Level Configurations
RAID Level
Configuration
0
Non-redundant striping mode
– Use this level for high-performance needs. RAID
Level 0 does not provide any data redundancy. RAID Level 0 stripes data across all of the
drives in the volume group. If a single drive fails, all of the associated volumes fail and all
data is lost. RAID Level 0 is suited for noncritical data. It is not recommended for
high-availability needs.
1
Striping mirroring mode
– RAID Level 1 uses drive mirroring to create an exact copy
from one drive to another drive. A minimum of two drives are required; one for the user
data, and one for the mirrored data. RAID Level 1 offers high performance and the best
data availability.
Data is written to two drives simultaneously. If one drive in a drive pair fails, the system
can instantly switch to the other drive without any loss of data or service. Only half of the
drives in the volume group are available for user data. If a single drive fails in a RAID
Level 1 volume group, all of the associated volumes become degraded, but the mirror
drive provides access to the data. RAID Level 1 can survive multiple drive failures as
long as no more than one failure occurs per mirrored pair. If a drive pair fails, all of the
associated volumes fail, and all data is lost.
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