HP Integrity rx4640 Server - Manual (Page 16)

Board Components and Features
— Multiple logical drives per array
Overview of Array Accelerator Features
The array accelerator is a high performance, battery-backed, 100-MHz SDRAM
DIMM cache module.
Array controllers use cache to store read data from the hard drives. The system can
later access this read data. The controller firmware uses the read-ahead and most
recently used caching algorithms.
Array controllers also use cache to complete drive write operations more quickly.
This use of the cache has further performance benefits:
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If the system requires data that still resides in write cache, the controller delivers
this data from the cache. This process is quicker than delivering the data from a
drive.
If the system writes new data to the same location, the controller overwrites the
cache contents. This eliminates a drive write operation.
If the system performs a RAID 1 procedure, the controller gets mirrored data
from the cache instead of from host memory.
If the system performs a RAID 5 procedure, the write cache collects enough data
blocks from several write accesses to carry out a full stripe write to the hard
drives. This operation eliminates the need to calculate and update parity
information each time that a data block is written to the drive.
With a battery-backed cache available, the array controller can complete the
following operations more rapidly:
Array capacity expansion—the expansion of a logical drive volume to include
more hard drives
Stripe size migration—the adjustment of the size of data blocks within a stripe,
done to improve performance
RAID level migration—the adjustment of RAID level to improve the fault
tolerance of the array
HP Smart Array 5300 Controller User Guide 1-5
HP CONFIDENTIAL
Writer: Kimberly Koch File Name: b-ch1 board components.doc
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