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Additional Raid Levels; Raid Configuration Strategies; Performance; Capacity Versus Fault-tolerance - HP xw4400 Mini White Paper

Software raid in linux workstations.
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Additional RAID Levels

More RAID levels can be created from the basic RAID levels by means of nesting. This is
accomplished by creating a second RAID array of other RAID disks, instead of creating a RAID of
physical disks. Nested RAID levels include RAID-0+1, a mirrored array of striped disks, RAID-10
(RAID-1+0), a striped array of mirrored disks, RAID-100 (RAID-10+0), which is a striped array of
RAID-10 arrays, RAID-5+0, RAID-0+5, and other combinations. In nested RAID solutions, it is
preferable to have a RAID-0 level on top to provide better performance as well as reducing the
number of disks that need to be regenerated when a disk fails. For example, RAID-10 is usually
preferred over RAID-0+1. Nested RAID levels are not supported by the Red Hat Enterprise Linux
installer, and must be configured manually. Software RAID-10 is the only additional RAID level
supported by HP Linux workstations.
Please note that while the Linux kernel allows for RAID-linear, -0, -1, -4, -5, and nested RAID levels, HP
only provides support for RAID-0, 1, 5, and 10.

RAID Configuration Strategies

Configuration of RAID workstations must take several factors into account in order to deliver optimal
performance, capacity, and redundancy. Note that the cost to implement RAID solutions increases as
desired performance, capacity, and redundancy increases. Users should consider the following when
designing an ideal RAID workstation:

Performance

Multiple factors must be taken into account, including both random and sequential read and write
speeds, latency times, and bus types; CPU and RAM configurations play a heavy part in the
performance of a software RAID solution as well. Such technical details are beyond the scope of this
document.

Capacity versus Fault-Tolerance

With most implementations of RAID, capacity and fault-tolerance are mutually exclusive.

Cost

Obviously, as the number of physical disks required for an installation increases, the cost also
increases.
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