HP-UX System Administrator's Guide: Routine Management Tasks

RAID 5 is a good choice where multitasking applications require a large history database
with a high read rate, or a database that uses a normal or less-than-normal percentage
of write operations, where writes are 33% or less of all I/O operations.
RAID 5 provides consistently high performance for large input/output operations,
greater or equal to 64 KB, but poor for smaller I/O sizes.
HP SureStore E Disk Array
HP SureStore E Disk Arrays provide high capacity and high speed mass storage with
continuous data availability, ease of service, scalability and connectivity. They are
designed to handle very large databases as well as data warehousing and data mining
applications since they have a huge data capacity, often measured in terabytes. They
are ideal for clustered configurations of HP-UX servers.
These disk arrays have no active single point of component failure. They utilize
component and function redundancy to provide full fault-tolerance for all
microprocessors, control storage, control and data busses, power supplies, and cooling
fans. Thus, they can sustain multiple component failures and still continue to provide
full access to stored data. However, a failure of a key component can degrade disk
array performance.
Using Hot Spared Disks
A hot spared disk drive is a disk that is reserved for swapping with a bad disk that
has no mirrored or parity data. It is simply a spare disk that is online and waiting for
a disk failure in a disk array. Use a hot spare if, in RAID 5, RAID 1/0, or RAID 1 groups,
high availability is so important that you want to regain data redundancy as soon as
possible if a disk module fails. A hot spare provides no data storage but enhances the
availability of each RAID 5, RAID 1, and RAID 1/0 group in a disk array. Disk arrays
keep hot spares in use all of the time.
NOTE: For disks managed by LVM, there is a similar feature called automatic sparing.
See HP-UX System Administrator’s Guide: Logical Volume Management for details.
An active hot spare is differentiated from traditional hot spares in that rebuild space
is distributed across all disks in the array for those disk arrays that provide active
spares. This allows user data to be stored on a “spare disk,” which improves I/O
performance. It also increases the amount of high performing RAID 1 space. In other
words, the active hot spare disk is constantly undergoing writes and reads in order to
verify that it is working properly.
In a traditional hot spare array, a defective hot spare disk may not be detected until it
is actually needed. The integrity of the active hot spare is assured because it is kept in
use at all times. Note that some disk arrays provide active hot spares although others
do not.
HP SureStore E Disk Array 209