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Chapter 4
Introduction to the
Intelligent Battery
Backup Unit
The intelligent Battery Backup Unit (iBBU) is for use with its high-
performance ServeRAID-MR10M SAS/SATA Controller. The battery
backup unit protects the integrity of the cached data on controller by
providing backup power if there is a complete AC power failure or a brief
power outage. The iBBU provides an inexpensive alternative to using an
uninterruptible power supply (UPS).
Writing a block of data to cache memory is much faster than writing it to
a storage device. The ServeRAID-MR10M controller then writes the
cached data to the storage device when system activity is low or when
the cache is getting full. The risk of using write-back cache is that the
cached data can be lost if the AC power fails before it has been written
to the storage device. This risk factor is eliminated when the controller
has an onboard iBBU.
The iBBU monitors the voltage level of the DRAM modules installed on
the ServeRAID-MR10M controller. If the voltage drops below a
predefined level, the battery backup module switches the memory power
source from the controller to the battery pack attached to the iBBU. As
long as the voltage level stays below the predefined value, the iBBU
provides power for memory. If the voltage level returns to an acceptable
level, the iBBU switches the power source back to the controller, and all
incomplete writes to storage devices are completed with no data loss.
An intelligent BBU has built-in functionality to charge the battery pack
automatically and to communicate battery status information such as
voltage, temperature, and current, to the host computer system.
ServeRAID-MR10M User's Guide
4-1
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