
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
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 |
| 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. |
Consistency Check An examination of the disk system to determine whether all conditions are valid for the specified configuration (such as parity.)
Cold Swap A cold swap requires that you turn the power off before replacing a defective hard drive in a disk subsystem.
Data Transfer Capacity The amount of data per unit time moved through a channel. For disk I/O, bandwidth is expressed in megabytes per second (MB/s).
Degraded A drive that has become
Disk A
Cont’d
Glossary129