Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Using High Availability Strategies
Disk Arrays Using RAID Data Protection Strategies
Appendix A950
Disk Arrays Using RAID Data Protection
Strategies
RAID stands for Redundant Arrays of Independent Disks. Various
configurations or RAID levels are available. We will mention several.
Mirroring (RAID Level 1)
In a RAID 1 configuration, all data is duplicated on two or more disks.
In hardware mirroring, each disk has a “twin,” a backup disk containing
an exact copy of its data. Some RAID 1 implementations duplicate not
only the disks but the array controller and the power supply as well.
In the case of software mirroring (discussed in “Using Software
Mirroring as a Disk Protection Strategy” on page 948), the original data
and its copied data may be spread over more than one disk as a result of
using LVM or VxVM software to manage your disk storage.
Pros and Cons
If a disk fails, the array controller will automatically switch all system
I/O activity to the drive containing the copy. This prevents the system
from going down in the event a drive fails. The disadvantage of hardware
mirroring is the expense of duplicating your hardware.
Recommended Uses and Performance Considerations
Use when high data availability is required. Can provide up to twice the
read I/0 rate although writes are similar to using single disks. The data
transfer rate is similar to using single disks.
Disk Striping (RAID Level 0)
This configuration interleaves data in blocks across multiple disks.
Pros and Cons
RAID 0 offers increased performance because several I/O transfers can
be done at the same time. However, it does not provide data redundancy
in the event of disk failure.