Glossary
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Disk Mirroring 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 system and reconstruct the failed disk.
Disk Spanning Several disks appear as one large disk using this
technology. This virtual disk can then store data across
disks with ease without the user being concerned about
which disk contains what data. The subsystem handles
this for the user.
Disk Striping Data is written across disks rather than on the same drive.
Segment 1 is written to drive 0, segment 2 is written to
drive 1, and so forth until a segment has been written to
the last drive in the chain. The next logical segment is
then written to drive 0, then to drive 1, and so forth until
the write operation is complete.
Duplexing This refers to the use of two controllers to drive a disk
subsystem. Should one of the controllers fail, the other is
still available to provide disk I/O. In addition, depending
how the controller software is written, both controllers
may work together to read and write data simultaneously
to different drives.
Fault-Tolerant When something is fault-tolerant it is resistent to failure.
A RAID 1 mirrored subsystem, for example, is
fault-tolerant because it can still provide disk I/O if one of
the disk drives in a mirrored system fails.
Hot Spare The “Hot Spare” is one of the most important features the
controller provides to achieve automatic, non-stop service
with a high degree of fault tolerance. This rebuild
operation will be carried out by the controller
automatically when a SCSI disk drive fails.
Logical Drive A set of contiguous chunks of a physical disk. Logical
disks are used in array implementations as constituents of
logical volumes or partitions. Logical disks are normally
transparent to the host environment, except when the
array containing them is being configured.
Mapping The conversion between multiple data addressing
schemes, especially conversions between member disk
block addresses of the virtual disks presented to the
operating environment by the array management
software.
Mirroring Refers to the 100% duplication of data on one disk drive
to another disk drive. Each disk will be the mirror image
of the other.