User's Manual

36 Understanding RAID Concepts
When choosing concatenation or a RAID level, the following performance
and cost considerations apply:
• Availability or fault-tolerance —Availability or fault-tolerance refers to a
system’s ability to maintain operations and provide access to data even
when one of its components has failed. In RAID volumes, availability or
fault-tolerance is achieved by maintaining redundant data. Redundant
data includes mirrors (duplicate data) and parity information
(reconstructing data using an algorithm).
•
Performance —Read and write performance can be increased or decreased
depending on the RAID level you choose. Some RAID levels may be more
appropriate for particular applications.
•
Cost efficiency —Maintaining the redundant data or parity information
associated with RAID volumes requires additional disk space. In situations
where the data is temporary, easily reproduced, or non-essential, the
increased cost of data redundancy may not be justified.
•
Mean Time Between Failure (MTBF) —Using additional disks to
maintain data redundancy also increases the chance of disk failure at any
given moment. Although this cannot be avoided in situations where
redundant data is a requirement, it does have implications for the
workload of your organization’s system support staff.
•
Volume —Volume refers to a single disk non-RAID virtual disk. You can
create volumes using external utilities like the O-ROM <Ctrl+R>.
Storage Management does not support the creation of volumes. However,
you can view volumes and use drives from these volumes for creation of
new virtual disks or Online Capacity Expansion (OCE) of existing virtual
disks, provided free space is available. Storage Management allows
Rename and Delete operations on such volumes.
For more information, see Choosing RAID Levels and Concatenation .