Avago Technologies AcceleRAID 170LP - Manual (Page 65)

Glossary
Manual No. DB11-000024-00 G-7
Disk Failure Detection
A RAID controller automatically detects SCSI disk failures. A monitoring
process running on the controller checks, among other things, elapsed time
on all commands issued to disks. A time-out causes the disk to be “reset”
and the command to be retried. If the command times out again, the
controller could take the disk “offline.” Mylex DAC960 controllers also
monitor SCSI bus parity errors and other potential problems. Any disk with
too many errors will also be taken “offline.” See also Offline.
Disk System
A storage system capable of supporting only disks.
Disk Traveling, Drive Traveling
A process that occurs when the drives are placed in a different order than the
original order. Disk traveling can occur whether or not a drive has failed.
Drive Groups, Drive Packs
A group of individual disk drives (preferably identical) that are logically tied
to each other and are addressed as a single unit. In some cases this may be
called a drive “pack” when referring to just the physical devices.
All the physical devices in a drive group should have the same size;
otherwise, each of the disks in the group will effectively have the capacity of
the smallest member. The total size of the drive group will be the size of the
smallest disk in the group multiplied by the number of disks in the group.
For example, if you have 4 disks of 400MB each and 1 disk of 200MB in a
pack, the effective capacity available for use is only 1000MB (5x200), not
1800MB.
Dual Active
A pair of components, such as storage controllers in a failure tolerant storage
system, that share a task or set of tasks when both are functioning normally.
When one component of the pair fails, the other takes the entire load. Dual
active controllers (also called Active/Active controllers) are connected to the
same set of devices and provide a combination of higher I/O performance
and greater failure tolerance than a single controller.