LSI MegaRAID Express 500 - Manual (Page 135)

Glossary 121
Glossary
Array A grouping or array of disk drives 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. A hot spare drive does not participate in 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 can also execute in a host computer. When it executes in a disk controller
or adapter, Array Management Software 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 each consist of the same number of disk drives. Array
spanning promotes RAID levels 1, 3, and 5 to RAID levels 10, 30, 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 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), it 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.
Channel An electrical path for the transfer of data and control information between a disk and a
disk controller.
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