Mylex DAC960PG, Installation Manual

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Glossary
Glossary-6 DAC960PG Installation Guide
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Note
The host operating system drivers and software
utilities remain unchanged regardless of the level of
RAID installed. The controller makes the physical
configuration and RAID level implementation
Replacement Table
A replacement table contains information regarding which SCSI devices
have been replaced by others through standby replacement.
Rotated XOR Redundancy
This term (also known as “parity”) refers to a method of providing complete
data redundancy while requiring only a fraction of the storage capacity of
mirroring. In a system configured under RAID 3 or RAID 5 (which require
at least three SCSI drives), all data and parity blocks are divided between the
drives in such a way that if any single drive is removed (or fails), the data on
it can be reconstructed using the data on the remaining drives. (XOR refers
to the Boolean “Exclusive-OR” operator.) In any RAID 3 or RAID 5 array,
the capacity allocated to redundancy is the equivalent of one drive.
SCSI Drive
A disk drive equipped with a SCSI interface (sometimes referred to as a
SCSI Disk). Each disk drive will be assigned a SCSI address (or SCSI ID),
which is a number from 0 to 7 (0 to 15 under Wide or Ultra SCSI). The SCSI
address uniquely identifies the drive on the SCSI bus or channel.
SCSI Drive States
Refers to a SCSI drive’s current operational status. At any given time, a
SCSI drive can be in one of five states: READY, ONLINE, STANDBY,
DEAD, or REBUILD.
The controller stores the state of the attached SCSI drives in its non-volatile
memory. This information is retained even after power-off. Hence, if a SCSI
disk is labeled DEAD in one session, it will stay in the DEAD state until a
change is made either by using a system level utility or after a rebuild. Each
of the states is described below: