HP NetRAID 1 Controller - Manual (Page 83)

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Replacement Disk: A disk available for use as or used to replace a failed member disk in a RAID
array.
Replacement Unit: A component or collection of components in a disk subsystem that are always
replaced as a unit when any part of the collection fails. Typical replacement units in a disk subsystem
includes disks, adapter logic boards, power supplies, and cables.
SCSI: (Small Computer System Interface) /skuh’zee/ A processor-independent standard for system-
level interfacing between a computer and intelligent devices, including hard disks, floppy disks, CD-
ROM, printers, scanners, etc. SCSI can connect up to 7 devices to a single adapter (or host adapter)
on the computer’s bus. SCSI transfers eight bits in parallel in narrow wide, or 16 bits in wide.
SCSI Channel: The HP NetRAID adapter controls the disk drives via SCSI-2 buses called
“channels” over which the system transfers data in either Fast/Wide or Ultra/Wide SCSI mode. The
NetRAID adapter has three channels and the NetRAID-1 adapter has one channel.
SCSI Disk Status: A SCSI disk module (physical drive) can be in one of these five states:
◊ Ready: a powered-on and operational disk that has not been configured
◊ Online: a powered-on and operational disk
◊ Hot Spare: a powered-on, stand-by disk ready for use if a disk fails
◊ Not Responding: the disk is not present, not powered-on, or has failed
◊ Rebuild: a disk to which one or more critical logical drives is restoring data
SCSI ID: Each SCSI device on an HP NetRAID SCSI bus must have a different SCSI address
number (Target ID, or TID) from 0 to 15, but not 7, which is reserved for the SCSI controller.
Drives IDs are determined by the slot positions. Consult your HP NetServer documentation and
chassis labels for the correct switch settings.
SNMP: (Simple Network Management Protocol) The Internet standard protocol developed to
manage nodes on an Internet Protocol (IP) network.
Spare: A hard drive available to back up the data of other drives.
Striping: Segmentation of logically sequential data, such as a single file, so that segments can be
written to multiple physical devices in a round-robin fashion. This technique is useful if the
processor is capable of reading or writing data faster than a single disk can supply or accept it. While
data is being transferred from the first disk, the second disk can locate the next segment. Data
striping is used in some modern databases and in certain RAID devices. In an inconsistent stripe,
firmware always updates the parity stripe to restore consistency.
Stripe Size: The amount of data contiguously written to each disk. Also called “stripe depth.” You
can specify stripe sizes of 4 KB, 8 KB, 16 KB, 32 KB, 64 KB, and 128 KB, for each logical drive.
For best performance, choose a stripe size equal to or smaller than the block size used by your host
operating system. A larger stripe depth produces higher read performance, especially if most of the
reads are sequential. For mostly random reads, select a smaller stripe width. You may specify a
stripe size for each logical drive.
Stripe Width: The number of disk modules across which the data are striped. The stripe width is
equivalent to the number of disks in the array.
Terminator: A resistor connected to a signal wire in a bus or network for the purpose of impedance
matching to prevent reflections, e.g., a 50 ohm resistor connected across the end of an Ethernet
cable. SCSI chains and some LocalTalk wiring schemes also require terminators.
Ultra/Wide-SCSI: An extension of SCSI-2, proposed by a group of manufacturers, which doubles
the transfer speed of Fast-SCSI to give 20 MB/s on an 8-bit connection and 40 MB/s on a 16-bit
connection.