Raid Performance Considerations; Configuring Red Hat Enterprise Linux With Software Raid - HP xw3400 User Manual

RAID Performance Considerations

With the many different RAID levels available, as well as the many more combinations provided by
nesting RAID levels, it can often be difficult to decide upon the most effective RAID configuration for
your needs. Since high performance speeds and data protection are almost always mutually exclusive
in RAID implementations, there will be a tradeoff to consider between these two factors. The following
are examples of different RAID configurations that will be more efficient in different situations.
If a filesystem had an external backup method, such as automated nightly tape backups, but
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needed to have quick read and write times, a RAID-0 configuration would make optimal use
of the disk and disk controller bandwidth, but not provide any data protection. RAID-0 is most
useful when performance is a key issue, but data protection is not as big a factor.
If it is necessary to have backup drives available at all time so there is no loss of data, even
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in case of a disk failure, a RAID-1 setup using several physical hard disks would provide a
good degree of redundancy so that no critical data is lost. This would be most valuable in a
system that depends highly upon data reliability and less upon higher disk speeds.
If a compromise between speed and redundancy is required, RAID-5 is fairly easy to
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implement, and provides a good balance between disk speeds and having parity data
available to rebuild the RAID array in case of failure. RAID-5 is moderately efficient in both
these areas, with neither being at a significant disadvantage, and is simpler to set up than a
nested RAID configuration.
The optimal RAID configuration for a particular system will depend on the specific needs of the
system; for example, how often will reads or writes have to be performed, versus how important is the
ability to survive in case of multiple disk failures? You may want to experiment with different
configurations to determine the RAID setup that works best for your system.

Configuring Red Hat Enterprise Linux with Software RAID

In order to configure software RAID on a workstation running Linux, you need to be using Linux
revision 2.4 or later.
Tip:
It is possible to configure software RAID with late 2.2.x or 2.0.x Linux
kernels if you have a matching RAID patch and version .90 of the
raidtools installed as well. The patch and the raidtools can both be
downloaded from http://people.redhat.com/mingo.
While it is possible to manually configure software RAID after a Linux system has been installed and
configured, it is HP's recommendation that software RAID should be configured at installation time.
The Red Hat Enterprise Linux installation utility includes a configuration tool to set up software RAID
partitions. Please note that while the Linux kernel itself allows for RAID-linear, -0, -1, -4, -5, and nested
RAID levels, the Anaconda installer only allows for RAID-0, -1, and -5.
The steps to configure software RAID using RHEL media are outlined below:
1. Power your HP workstation; boot to your RHEL installation media.
2. Continue through the installation until the "Disk Partitioning Setup" screen.
3. Select "Manually partition with Disk Druid."
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