Users Guide

Organizing data storage for availability and performance
RAID provides different methods or RAID levels for organizing the disk storage. Some RAID levels maintain redundant data so
that you can restore data after a disk failure. Different RAID levels also entail an increase or decrease in the I/O (read and write)
performance of a system.
Maintaining redundant data requires the use of additional physical disks. The possibility of a disk failure increases with an
increase in the number of disks. Since the differences in I/O performance and redundancy, one RAID level may be more
appropriate than another based on the applications in the operating environment and the nature of the data being stored.
When choosing a RAID level, the following performance and cost considerations apply:
●
Availability or fault-tolerance — Availability or fault-tolerance refers to the ability of a system 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 option cannot be avoided in situations where redundant data is a requirement, it
does have implications on the workload of the system support staff within your organization.
● 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.
Choosing RAID levels
You can use RAID to control data storage on multiple disks. Each RAID level or concatenation has different performance and
data protection characteristics.
NOTE: The H3xx PERC controllers do not support RAID levels 6 and 60.
The following topics provide specific information on how each RAID level store data as well as their performance and protection
characteristics:
● Raid level 0 (striping)
● Raid level 1 (mirroring)
● Raid level 5 (striping with distributed parity)
● Raid level 6 (striping with additional distributed parity)
● Raid level 50 (striping over raid 5 sets)
● Raid level 60 (striping over raid 6 sets)
● Raid level 10 (striping over mirror sets)
RAID level 0 - striping
RAID 0 uses data striping, which is writing data in equal-sized segments across the physical disks. RAID 0 does not provide data
redundancy.
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Managing storage devices