HP Smart Array Cluster Storage System

Component Identification
1-14 HP Smart Array Cluster Storage System User Guide
HP CONFIDENTIAL
Writer: Rob Weaver File Name: b-ch1 Component Identification
Codename: Aurora Part Number: 240333-003 Last Saved On: 11/6/02 1:03 PM
Battery-Backed Cache Module Overview
The battery-backed cache module is a high-performance, 100-MHz SDRAM DIMM
read/write cache that increases performance in database and fault-tolerant
configurations.
Caching Functions
To enable faster data access from disk storage, the cache module performs two types
of caching:
• Posted-write caching—the controller writes user data in the cache memory on the
module rather than directly to the drives. Later, when the system is idle, the
controller writes the data to the drive array.
• Read-ahead caching—the controller detects sequential array access, reads ahead
into the next sequence of data, and stores the data in the read-ahead cache. Then,
if the next read access is for the cached data, the controller immediately loads the
data into system memory, avoiding the latency of a disk access.
Batteries
The cache module has two rechargeable and replaceable NiMH battery packs that
protect cached data during equipment failure or power outage:
• Up to 3 days protection for 256-MB cache DIMMs
• Up to for 4 days protection for 128-MB cache DIMMs
Under normal operating conditions, the battery packs should operate for 3 years
before replacement is necessary. The batteries recharge continuously when the
system is powered on.
NOTE: Temperature, age, and cache size may affect battery life.
The batteries also preserve data when you remove the cache module from the
controller. After you reinstall the cache module, and power is restored, the
initialization process writes the preserved data to the array. This feature is important
for data stored in the posted-write cache, but not yet written to an array.