IBM ServeRAID M5014, User Manual

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ServeRAID M5014/M5015 SAS/SATA Controller User’s Guide 4-1
Chapter 4
Intro to the ServeRAID
M5000 Series Battery
Assembly
The ServeRAID M5000 Series Battery Assembly is for use with the high-
performance ServeRAID M5015 controller. The battery backup unit
(BBU) 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 ServeRAID M5000 Series Battery Assembly 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 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 battery
assembly.
The ServeRAID M5000 Series Battery Assembly monitors the voltage
level of the DRAM modules installed on the 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 battery assembly. As long as the voltage level stays below the
predefined value, the battery assembly provides power for memory. If the
voltage level returns to an acceptable level, the battery assembly
switches the power source back to the controller, and all incomplete
writes to storage devices are completed with no data loss.
The ServeRAID M5000 Series Battery Assembly 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.