HP-UX System Administrator's Guide: Overview

Disk Striping
Disk striping spreads data over multiple physical devices in such a way that successive
writes occur on different devices. In this way, the second chunk of data to be written
does not have to wait for the device writing the first chunk to finish. In essence, if you
have n devices striped together, then you can write n chunks of data simultaneously
(or nearly simultaneously) without having to wait for devices to become ready for
subsequent data.
Striping can be performed at the device level if you are using a disk array, RAID array,
or other hardware that supports RAID operations. Other types of disks striping can be
performed by LVM or the VERITAS Volume Manager (VxVM). For information about
performing striping using one of the volume managers, see lvcreate(1M) or vxassist(1M).
You can specify the size of data chunks to use with striping.
Hardware data striping is accomplished by using certain RAID configurations. Striping
related RAID levels commonly used on HP disk arrays that support RAID are:
RAID 0 Striping using data blocks with no parity disks in the stripe. For performance
reasons, data blocks are usually a multiple of 512 bytes (the physical sector
size of most hard disks).
An important consideration when using RAID 0 is the number of disks in
the stripe. The more disks you have in the stripe, the greater the chance of
one of them failing. With no parity disk included in the stripe, missing data
cannot be reconstructed and therefore must be restored from a backup or
other source.
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.
Storage on HP-UX 55