HP NetRAID 1 Controller - Manual (Page 79)

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Glossary
Array: An array of disk modules combines the storage space on the disk modules into a single
segment of contiguous storage space. The HP NetRAID adapter can group disk modules on one or
more of its SCSI channels into an array. A hot spare disk module does not participate in an array.
Array Management Software: Software that provides common control and management for a disk
array. Array Management Software most often executes in a disk adapter or intelligent host bus
adapter, but can also execute in a host NetServer. When it executes in a disk adapter or adapter,
Array Management Software is an embedded utility.
Array Spanning: Array spanning by a logical drive combines storage space in two arrays of disk
modules into a logical drive’s single, contiguous storage space. logical drives of the HP NetRAID
adapter can span two consecutively numbered arrays that each consist of the same number of disk
modules. Array spanning promotes RAID levels 1, 3, and 5 to RAID levels 10, 30, and 50,
respectively.
Asynchronous Operations: Operations that bear no relationship to each other in time and can
overlap. The concept of asynchronous I/O operations is central to independent access arrays in
throughput-intensive applications.
BIOS: (Basic Input/Output System) The part of the operating system of the computer that provides
the lowest level interface to peripheral devices. The HP NetRAID BIOS resides in the adapter.
Cache I/O: A small, fast memory holding recently-accessed data, designed to speed up subsequent
access to the same data. It is most often applied to processor-memory access but also used for a local
copy of data accessible over a network etc. When data is read from, or written to, main memory a
copy is also saved in the cache, along with the associated main memory address. The cache monitors
the addresses of subsequent reads to see if the required data is already in the cache. If it is (a cache
hit), then it is returned immediately and the main memory read is aborted (or not started). If the data
is not cached (a cache miss), then it is fetched from main memory and also saved in the cache.
Channel: An electrical path for the transfer of data and control information between a disk and a
disk adapter.
Cold Swap: Replacing a defective hard drive in a disk subsystem that requires the power be turned
off to do the substitution.
Consistency Check: An examination of the disk system on a stripe-by-stripe basis to verify if data
and parity are valid. Inconsistent data or parity will be repaired if enough redundant/valid data
remains.
Data Transfer Capacity: The amount of data per unit time moved through a channel. For disk I/O,
bandwidth is expressed in megabytes per second (MB/s).
dB: A decibel; a logarithmic unit of measure of sound.
Degraded: A logical drive that has decreased in performance due to a failed physical drive.
Disk: A non-volatile, randomly addressable, rewritable mass storage device, including both rotating
magnetic and optical disks and solid-state disks, or non-volatile electronic storage elements.
Disk Array: A collection of disks from one or more disk subsystems combined with array
management hardware and software. It controls the disks and presents them to the operating system
as one or more logical disks.
Disk Duplexing: A variation on disk mirroring where, as well as redundant disk drives, a second
disk adapter or host adapter is also present.