HP D5970A - NetServer - LCII Installation And Configuration Manual page 140

Glossary
the system. If a single disk fails, it can be rebuilt from the parity of the respective
data on the remaining disks.
Physical Disk Roaming: The ability of an adapter to keep track of a hot swap
disk module that has been moved to a different slot in the hot swap cages. Both
slots must be controlled by the same adapter.
Power Fail Safeguard: When this setting is enabled, during a reconstruction
process (not a rebuild) a copy of the data that is being restructured will always be
stored on disk, so that if a power failure occurs during the reconstruction, there
will be no risk of data loss.
Power-on Rights: These settings specify how a logical drive can be accessed by
the controller. These settings may be used in clustering setups where more than
one controller is sharing a logical drive, or to control local logical drive access.
The None selection specifies that this controller will have no access rights to the
logical drive. The Read setting specifies that this controller will have read only
access to the logical drive. The Read+Write setting allows both read and writes to
the logical drive. The All setting allows read, write, rebuild, consistency checks,
and so on.
RAID: Redundant Array of Independent Disks (originally Redundant Array of
Inexpensive Disks) is an array of multiple small, independent hard disk drives
that yields performance exceeding that of a Single Large Expensive Disk
(SLED). A RAID disk subsystem improves I/O performance using only a single
drive. The RAID array appears to the host HP NetServer as a single storage unit.
I/O is expedited because several disks can be accessed simultaneously.
RAID Levels: A style of redundancy applied to a particular logical drive. It may
increase the fault tolerance and performance of the logical drive, and it may
decrease its usable capacity. Each logical drive must have a RAID level assigned
to it.
RAID levels 1, 3, and 5 are for logical drives that occupy a single array (non-
spanned array). Table 2-1 in Chapter 2 describes RAID levels for logical drives
that do not span arrays. Briefly,
RAID 0 has no redundancy. It requires one or more physical drives.
RAID 1 has mirrored redundancy. It requires two physical drives in an
array.
RAID 3 has parity redundancy with a dedicated parity disk. It requires
three or more physical drives in an array.
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