IBM Redbooks ServeRAID-MR10i, Руководство пользователя

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ServeRAID-MR10i User’s Guide 4-1
Chapter 4
Introduction to the
Intelligent Backup Bat-
tery Unit
IBM
®
provides the intelligent Battery Backup Unit (iBBU) for use with its
high-performance ServeRAID-MR10i SAS/SATA Controller. The battery
backup unit protects the integrity of the cached data on RAID 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-MR10i 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 ServeRAID-
MR10i controller has an onboard iBBU.
The iBBU monitors the voltage level of the DRAM modules installed on
the ServeRAID-MR10i controller. If the voltage drops below a predefined
level, the battery backup module switches the memory power source
from the controller 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.