Lenovo ThinkServer RD330 MegaRAID SAS Software User Guide - Page 391

MegaRAID SAS Software User Guide Appendix C: Glossary | Appendix C Glossary This appendix provides a glossary for terms used in this document. access policy alarm enabled alarm present array BBU present BGI rate BIOS cache cache flush interval caching capacity coerced capacity coercion mode A virtual drive property indicating what kind of access is allowed for a particular virtual drive. The possible values are Read/Write, Read Only, or Blocked. A controller property that indicates whether the controller's onboard alarm is enabled. A controller property that indicates whether the controller has an onboard alarm. If present and enabled, the alarm is sounded for certain error conditions. See drive group. A controller property that indicates whether the controller has an onboard battery backup unit to provide power in case of a power failure. A controller property indicating the rate at which the background initialization of virtual drives will be carried out. Basic Input/Output System. The computer BIOS is stored on a flash memory chip. The BIOS controls communications between the microprocessor and peripheral devices, such as the keyboard and the video controller, and miscellaneous functions, such as system messages. Fast memory that holds recently accessed data. Use of cache memory speeds subsequent access to the same data. 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. A controller property that indicates how often the data cache is flushed. The process of using a high speed memory buffer to speed up a computer system's overall read/write performance. The cache can be accessed at a higher speed than a drive subsystem. To improve read performance, the cache usually contains the most recently accessed data, as well as data from adjacent drive sectors. To improve write performance, the cache can temporarily store data in accordance with its write back policies. A property that indicates the amount of storage space on a drive or virtual drive. A drive property indicating the capacity to which a drive has been coerced (forced) to make it compatible with other drives that are nominally the same capacity. For example, a 4-GB drive from one manufacturer might be 4,196 MB, and a 4-GB from another manufacturer might be 4,128 MB. These drives could be coerced to a usable capacity of 4,088 MB each for use in a drive group in a storage configuration. A controller property indicating the capacity to which drives of nominally identical capacity are coerced (forced) to make them usable in a storage configuration. Page 391