Array Accelerator - Compaq 219700-001 - ProLiant - 1500 Reference Manual

D-13
Figure D-8. Data Striping distributes data across all physical drives

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
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