2 Glossary
Controller
A computer module that interprets signals between a host and a peripheral device.
CRC (cyclic redundancy check)
An error correcting code used in Fibre Channel
D
Disconnect/Reconnect
Disconnect is a function that allows a target SCSI device (typically a disk drive that
received a request to perform a relatively long I/O operation) to release the SCSI bus so that
the controller can send commands to other devices. When the operation is complete and the
SCSI bus is needed by the disconnected target again, it is reconnected.
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.
F
Fabric
A group of interconnections between ports that include a fabric element.
Fault-Tolerant
When something is fault-tolerant it is resistant 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.
F_Port
A port in the fabric where an N_port or NL_port may attach.
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