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MegaRAID SCSI 320-2 Hardware Guide C-1
Copyright © 2002 by LSI Logic Corporation. All rights reserved.
Appendix C
Glossary
Array A grouping of individual disk drives that combines the storage space on
the disk drives into a single segment of contiguous storage space.
MegaRAID can group disk drives on one or more SCSI channels into an
array.
Array
Management
Software
Software that provides common control and management for a disk array.
Array management software most often executes in a disk controller or
intelligent host bus adapter, but it can also execute in a host computer.
When array management software executes in a disk controller or
adapter, it is often called firmware.
Array Spanning Array spanning by a logical drive combines storage space in two arrays
of disk drives into a single, contiguous storage space in a logical drive.
MegaRAID logical drives can span consecutively numbered arrays that
have the same number of disk drives. Array spanning promotes RAID
levels 1 and 5 to RAID levels 10 and 50, respectively. See also Disk
Spanning.
Asynchronous
Operations
Operations that bear no relationship to each other in time and can
overlap. The concept of asynchronous I/O operations is central to
independent access arrays in throughput-intensive applications.
Cache I/O A small amount of fast memory that holds recently accessed data.
Caching speeds subsequent access to the same data. It is most often
applied to processor-memory access, but it can also be used to store a
copy of data accessible over a network. When data is read from or
written to main memory, a copy is also saved in cache memory with the
associated main memory address. The cache memory software monitors
the addresses of subsequent reads to see if the required data is already
stored in cache memory. If it is already in cache memory (a cache hit),
the data is read from cache memory immediately and the main memory
read is aborted (or not started.) If the data is not cached (a cache miss),
it is fetched from main memory and saved in cache memory.