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Glossary
Manual No. 775051 G-11
Logical Drive States
A logical (system) drive can be Online, Critical, or Offline. Notice that the
term “online” is used for both physical and logical drives.
LVD
Low Voltage Differential, a form of SCSI signaling introduced with Ultra2
SCSI (Fast40 SCSI) uses data high and data low signal lines to increase
transmission distances over those of single-ended (conventional SCSI
signaling) lines. LVD allows for cable lengths of up to 12 meters
(approximately 39 feet) with up to 15 devices. LVD also lowers noise, power
usage, and amplitude.
LVD differs from conventional differential signaling in that only positive and
negative values are distinguished, not voltage levels. Other advantages are
that LVD devices consume less power and can sense single-ended devices on
the bus and revert to single-ended signaling. Devices need to be Ultra2 SCSI
LVD devices in order to take advantage of the LVD signaling. Mylex
AcceleRAID, eXtremeRAID, and DAC FL controllers are LVD controllers.
Megabit
A million bits; used as a common unit of measure, relative to time in
seconds, as an expression of a transmission technology's bandwidth or data
transfer rates. Megabits per second (Mbps) is a frequent measure of
bandwidth on a transmission medium.
Megabyte
2
20
(1,048,576) bytes. One megabyte can store more that one million
characters. Abbreviated as M or MB.
Mirrored Cache
A cache memory that has duplicate data from another controller. In the event
of failure of the original controller, the second controller can take the cached
data and place it on the disk array.
Mirrored Hard Drive
Two hard drives the computer sees as one unit. Information is stored
simultaneously on each drive. If one hard disk drive fails, the other contains
all of the cached data and the system can continue operating.