LSI Series 518 Appendix C Glossary

Appendix C Glossary

Array

Management

Software

Array Spanning

Asynchronous Operations

Cache I/O

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.

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 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.

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.

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.

MegaRAID SCSI 320-2 Hardware Guide

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