HP A7143A RAID160 SA Controller Support Guide

Glossary
fault tolerance
Glossary166
fault tolerance The ability of a server to
recover from hardware problems without
interrupting server performance or
corrupting data. Hardware RAID is most
commonly used, but there are other types of
fault tolerance—for example, controller
duplexing and software-based RAID.
flashing Updating the flash memory on a
system. Flash memory is non-volatile
memory that is used to hold control code
such as BIOS information. It is also very fast
because it can be rewritten block by block,
rather than byte by byte.
hot spare See online spare.
interim data recovery If a drive fails in
RAID 1, 1+0, 5 or ADG, the system will still
process I/O requests, but at a reduced
performance level.
logical drive (or logical volume) A group
of physical drives, or part of a group, that
behaves as one storage unit. Each
constituent physical drive contributes the
same storage volume to the total volume of
the logical drive. Has performance
advantages over individual physical drives.
logical drive capacity extension See
capacity extension.
LVD (low voltage differential) A type of
SCSI signaling that allows a maximum
transfer rate of either 80 MB/s or 160 MB/s,
conforming to either the Wide Ultra2 or
Wide Ultra160 SCSI standards respectively.
online spare Also known as a hot spare,
this is a drive in a fault-tolerant system that
normally contains no data. When any other
drive in the array fails, the controller
automatically rebuilds the missing data that
was on the failed drive onto the online spare.
The controller constructs the missing data
from the duplicate or parity data that is on
the remaining drives in the array.
PCI-X An enhanced PCI bus that allows
operation at 133 MHz, equivalent to a data
throughput of 1.0 GB/s. PCI-X is
backward-compatible with PCI systems and
devices, which operate at 66 MHz or
33 MHz.
RAID (Redundant Array of
Independent Disks) A form of fault
tolerance. RAID 0 (no fault tolerance) uses
data striping to distribute data evenly across
all physical disks in the array, but has no
redundant data. RAID 1+0 (drive mirroring)
duplicates data from one drive onto a second
drive. RAID 5 (distributed data guarding)
distributes parity data across all drives in
the array, and uses the parity data and data
on remaining drives to reconstruct data from
a failed drive. RAID ADG (advanced data
guarding) is similar to RAID 5, but uses two
independent sets of parity data. Refer to
Appendix D for more details.
rebuild See Automatic Data Recovery.
SCSI ID A unique ID number assigned to
each SCSI device connected to a SCSI bus.
The ID number determines the device
priority on the SCSI bus; ID 7 is the highest
priority and is always assigned to the SCSI
controller.
SE (single-ended) A type of SCSI
signaling that allows a maximum transfer
rate of 40 MB/s. Conforms to the Wide-Ultra
SCSI standard. Now being phased out in
favor of LVD technology.