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.

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:

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.

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

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

increases.

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