HP-UX System Administrator's Guide: Overview HP-UX 11i v3 (B3921-90011, September 2010)

• Do you need off site copies of your data?
• How often do the data change?
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
• HP-UX 11i v3 HA-OE
• HP-UX 11i v3 DC-OE
Mirrordisk/UX supports up to three copies of data if you are using LVM with Version 1 volume
groups, and up to six copies of data if you are using LVM with Version 2 volume groups.
Using the base version of VERITAS Volume Manager you can mirror only your root file system.
By purchasing and installing the full version of VERITAS Volume Manager, you can mirror other
disk groups and have up to 32 mirror copies of a volume’s address space.
50 Major Components of HP-UX