Dot Hill Systems SANnet II 200 - Manual (Page 32)

hot spare or hot
sparing A drive in a RAID 1 or RAID 5 configuration that is held in reserve to replace any other
drive that fails. After a reconstruction, the hot-spare drive is returned to the standby status.
hot-serviceable The ability to remove, replace or add a device while power is still applied but all I/O
processes are suspended.
hot-swappable The ability of a field-replaceable unit (FRU) to be removed and replaced while the array
remains powered on and operational.
ID Identifier number
IEC International Electrotechnical Commission
initialization The process of writing a specific pattern to all data blocks on all drives in a logical drive.
This process overwrites and destroys existing data on the disks and the logical drive.
Initialization is required to make the entire logical drive consistent at the onset.
Initialization ensures that any parity checks performed in the future will execute correctly.
IOPS Input/output operations per second. A measure of I/O performance, this is usually used to
quote random I/O performance. See throughput.
JBOD Just a Bunch Of Disks. JBOD refers to a group of drives without an embedded RAID
controller; generally, such a group is used without RAID formatting, with a host-based
hardware RAID controller, or with RAID formatting from host software (with no
hardware-base RAID controller)
LAN Local Area Network
LD Logical drive
logical drive A section of disk storage space, also referred to as a LUN, that is presented to the host
operating environment as a single physical drive. A logical drive may be located on one or
more physical drives. Each array controller can manage one to eight logical drives
LUN Logical unit number. A LUN is a set of physical drives in a RAID configuration that are
seen by the operating system as one virtual drive.
LUN mapping The ability to change the virtual LUN as presented to the server from storage. This enables
such benefits as the ability of a server to boot from the SAN without requiring of a local
disk drive. Each server requires LUN 0 to boot.
LUN masking The characteristic that enables an administrator to dynamically map an HBA to a specified
LUN. This provides an individual server or multiple servers access to an individual drive
or to multiple drives, and prohibits unwanted server access to the same drives.
LVD A low-noise, low-power, and low-amplitude signaling technology that enables data
communication between a supported server and storage devices. LVD signaling uses two
wires to drive one signal over copper wire and requires a cable that is no longer than 25
meters (82 ft.).
MB Megabyte. 1,000,000 bytes or characters of data.
mirroring: RAID 1 Data written to one disk drive is simultaneously written to another disk drive. If one disk
fails, the other disk can be used to run the array and reconstruct the failed disk. The
primary advantage of disk mirroring is 100% data redundancy. Since the disk is mirrored,
it does not matter if one of the disks fails. Both disks contain the same data at all times and
either can act as the operational disk. Disk mirroring provides 100% redundancy, but is
expensive because each drive in the array is duplicated.
MTBDL Mean time between data loss. In a RAID system, this is the average expected time
between two rapid disk failures that would cause irreparable data loss.
MTBF Mean time between failures. A measure of reliability, this is the average expected time
between failures of equipment, usually measured in operating hours.
MTTR Mean time to repair. A measure of availability, this is the average time the system is out of
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