HP ProLiant 1500 SMART-2DH Array Controller Reference Guide - Page 146

Figure D-8. Data Striping distributes data across all physical drives D-13 Array Accelerator By serving as a posted write cache and read-ahead cache, the SMART-2DH Controller Array Accelerator dramatically improves the performance of read and write commands. The Array Accelerator is particularly useful for increasing performance in database and fault-tolerant configurations. Performance The Array Accelerator increases performance by having SMART-2DH Controller write data to the cache memory on the Array Accelerator rather than directly to the drives. The system can access this cache memory more than 100 times faster than accessing disk storage. The SMART-2DH Controller writes the data in the Array Accelerator to the drive array at a later time, when the controller is otherwise idle. The controller also uses the Array Accelerator to increase performance by anticipating requests. The Array Accelerator uses a multi-threaded algorithm to predict the next likely read operation for the array. That data is pre-read into the Array Accelerator and therefore is ready before you access it. When the SMART-2DH Array Controller receives a read request for the cached data, it can be burst immediately into system memory at PCI bus speeds. Data Protection The Array Accelerator was designed to protect data integrity. Batteries and ECC memory protect the cache memory. This allows users to take full advantage of the performance without sacrificing reliability. The Array Accelerator was also designed to be removable as a complete unit. This, along with the integrated batteries, means that the Array Accelerator may be removed from one SMART-2DH Controller and installed on another. If there is any data in the Array Accelerator that has not been written to the hard drive, it may be physically transferred to another SMART-2DH Controller. This might happen if the SMART-2DH Controller or server failed before the cached data could be stored on a drive. SMART-2DH Array Controller Reference Guide Writer: Pamela King Project: SMART-2DH Array Controller Reference Guide Comments: 295469-002 File Name: K-APPD.DOC Last Saved On: 2/27/98 12:06 PM COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED