HP NetRAID 1 Controller - Manual (Page 80)

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Disk Mirroring: Writing duplicate data to more than one (usually two) hard disks, in order to
protect against loss of data in the event of device failure. It is a common feature of RAID systems.
Disk Spanning: Disk spanning allows multiple disk drives to function like one big drive. Spanning
not only overcomes disk space shortage; it also simplifies storage management by combining
existing resources or adding relatively inexpensive resources. For example, four 400 MB disk drives
can be combined to appear to the operating system as one single 1600 MB drive. Spanning alone
does not provide reliability or performance enhancements. Spanned logical drives must have the
same stripe size and must be contiguous. For example logical drives 1 and 2 can be spanned; logical
drives 1 and 3 cannot.
Disk Striping: A method of data management in which data is separated into consecutive stripes of
data and mapped round-robin to consecutive physical drives.
Disk Subsystem: A collection of disks and the hardware that connects them to one or more host
NetServers. The hardware can include an intelligent adapter, or the disks can attach directly to a host
NetServer I/O bus adapter.
Double Buffering: A technique that achieves maximum data transfer bandwidth by constantly
keeping two I/O requests for adjacent data outstanding. A software component begins a double-
buffered I/O stream by issuing two requests in rapid sequence. Thereafter, each time an I/O request
completes, another is immediately issued. If the disk subsystem is capable of processing requests fast
enough, double buffering allows data to be transferred at the full-volume transfer rate.
Failed Drive: A drive that has ceased to function, or consistently functions improperly.
Fast SCSI: A variant on the SCSI-2 bus. It uses the same 8-bit bus as the original SCSI-1, but runs
at up to 10MB/s, i.e., double the speed of SCSI-1.
Firmware: Software stored in read-only memory (ROM) or Programmable ROM (PROM).
Firmware is responsible for the behavior of a system when it is first switched on.
Format: The process of writing zeroes to all data fields in a physical drive (hard drive) and to map
out unreadable or bad sectors. Because most hard drives are factory formatted, formatting is usually
only done if a hard disk generates several media errors.
GB: A gigabyte; 1,073,741,824 (2 to the 30th power) bytes.
Host Computer: Any computer to which disks are directly attached. Mainframes, servers,
workstations, and personal computers can all be considered host computers.
Hot Spare: An idle, powered/on stand-by disk module ready for use should another disk module
fail. It does not contain any user data. Up to eight disk modules can be assigned as hot spares for an
adapter. A hot spare can be dedicated to a single array, or it can be part of the global hot-spare pool
for all the arrays controlled by the adapter. Only one hot spare can be dedicated to a given array.
When a disk fails, the adapter’s firmware automatically replaces and rebuilds the data from the failed
disk onto the hot-spare disk. Data can only be rebuilt from logical drives with redundancy (RAID
levels 1, 3, 5, 10, 30, or 50; not RAID 0), and the hot spare-disk must have sufficient capacity. The
system administrator can replace the failed disk module and designate the replacement disk module
as a new hot spare.
Hot Swap: The substitution of a replacement unit in a disk subsystem for a defective one, where the
substitution can be performed while the subsystem is running (performing its normal functions). Hot
swaps are manual.
Hot Swap Disk Module: Hot swap modules allow a system administrator to replace a failed disk
drive in a server without powering down the server and suspending network services. The hot swap
module simply pulls out from its slot in the drive cage because all power and cabling connections are
integrated into the server backplane. Then the replacement hot swap module can slide into the slot.
Hot swapping only works for RAID 1, 3, 5, 10 30 and 50 configurations.