HP-UX System Administrator's Guide: Overview

Establishing Multiple Paths to a Device (for redundancy)
One of the key points to protecting your data is eliminating single points of failure.
RAIDs and other Disk Arrays, Disk Mirroring, and Data Backups, and Serviceguard
are all about eliminating single points of failure.
Beginning with HP-UX 11i version 3, HP-UX 11i supports device multipathing, a
technology that associates device files with devices by using unique device IDs rather
than the hardware path to the devices. This means that a single device file can represent
multiple hardware paths to a given device which, when combined with hardware that has
multiple ports (supporting multiple physical connections), yields not only greater I/O
bandwidth but also redundant paths to the device. HP-UX 11i can now automatically
failover to an alternate hardware path should an interface card, cable, or other piece
of hardware fail, and it can do this with little or no interruption to applications and
users accessing the device.
RAIDs and other Disk Arrays
Disk arrays, and collections of independent disks configured using RAID configurations
are capable of mirroring data from one physical disk to one or more additional physical
disks, thereby giving you additional copies of the data should one drive mechanism
fail. Simply having a second copy of the data exponentially decreases the chance of a
failure of all copies of your data.
Hardware data mirroring is accomplished by using certain RAID configurations.
Mirroring related RAID levels commonly used on HP disk arrays that support RAID
are:
RAID 1 Mirroring data to one or more additional disks provides redundancy and
the ability to take a copy of your data offline for example to snapshot the
current state of the disk to a backup set for offline/off site storage.
NOTE: Not every device supports every RAID level. Check the hardware
documentation for your disk arrays, RAID arrays, disk drives, or other storage
equipment for information about which RAID levels are supported by your devices.
Disk Mirroring
The previous section discussed disk arrays and RAID configurations primarily from a
hardware perspective. Disk mirroring can also be accomplished in software. The volume
managers LVM and VERITAS Volume Manager can be used to mirror data.
In order to implement disk mirroring using LVM, you need to install the MirrorDisk/UX
product (which is available as an optional product in the following Operating
Environments):
• HP-UX 11i v3 BOE
• HP-UX 11i v3 VS-OE
Storage on HP-UX 57