Software RAID in Linux Workstations

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

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 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 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.”