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

RAID 5 Striping using data blocks with parity information evenly distributed across the
devices in the stripe set. The parity information can be used to reconstruct the missing
data if a drive should fail.
The stripe set can function with one missing drive and, when the failed drive is
replaced, the parity information on the remaining drives can be used to reconstruct
the missing data (formerly on the failed drive). Once reconstruction is complete, the
new disk drive fully participates in the set to help protect against data loss should a
different drive fail later on.
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.
Distributing Disk Access
For the same reasons as described in Disk Striping, the more you can balance disk access, the
better performance you will achieve from disk reads and writes. This reduces the chance that a
given device will be busy servicing another data access operation, causing additional reads and
writes to wait.
File System Type
Your choice of file system type can also affect the efficiency of accessing your data. The VERITAS
File System (VxFS) is generally faster than using the HFS file system.
Establishing Multiple Paths to a Device (for efficiency)
Beginning with HP-UX 11i version 3, HP-UX 11i supports device multipathing, a new 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 redundant paths to the device, but greater I/O bandwidth.
HP-UX 11i version 3 can automatically load balance between multiple physical connections to
a device, improving I/O efficiency.
For more information on device multipathing, see “How Storage is Addressed” (page 51).
Disk Mirroring (for performance)
Though the topic of disk mirroring is more of a data redundancy topic, there are performance
reasons for mirroring. If you use a RAID 1 (mirroring) disk configuration in an environment
more focused on reading data from the disks rather than writing data to the disks in the mirror,
you can significantly speed up data input because subsequent disk blocks can be retrieved in
parallel from alternating devices. For additional benefits of using RAID 1 configurations, see
“Disk Mirroring”.
Storage and Data Redundancy
The value of most data in the information age ranges from important to critical. The importance
of data redundancy is directly proportional to the importance of the data being protected.
Data redundancy can take many forms but in every form multiple copies of your data exist so
that if the primary copy of the data is damaged or destroyed another copy of those data can be
used to continue your operations.
When choosing a data redundancy technology consider the following:
• How quickly do you need to recover from data loss?
• How easy is it to switch over to the alternate copy of your data should the primary become
unusable?
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