Avago Technologies Cache Protection for RAID Controller Cards - Manual (Page 5)

Avago Technologies
- 5 -
Cache Backup Products for MegaRAID SAS+SATA RAID Controllers User Guide
May 2015 Chapter 1: Introduction
Overview
Chapter 1: Introduction
This guide documents the Avago® family of MegaRAID® cache backup products that are used with its
high-performance MegaRAID SAS+SATA RAID controllers to protect cached data. It describes the products,
documents the installation instructions, and provides the technical specifications.
The cache backup products documented in this guide include the following:
 intelligent Battery Backup Units (iBBU units)
 intelligent Transportable Battery Backup Units (iTBBU units)
 Transportable Memory Modules (TMMs)
 RAID Cache Module (RCM01)
 CacheVault® Flash Modules (CVFMs)
 CacheVault Power Modules (CVPMs)
1.1 Overview
The battery backup units and the memory modules protect the integrity of the cached data on MegaRAID controllers
by providing backup power if there is a complete AC power failure or a brief power outage. These products provide an
alternative to using an uninterruptible power supply (UPS), and a second level of fault tolerance when used in
conjunction with a UPS.
1.1.1 Benefits
The cache memory available on MegaRAID controllers can improve overall system performance, because writing data
to the controllers cache memory is much faster than writing it to a storage device. Write operations appear to
complete very quickly at the software application level. The RAID 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. You can use an onboard transportable memory module in conjunction with an iBBU unit or a
CVPM module, and a CVFM module in conjunction with a CVPM module to eliminate this risk.
1.1.2 Intelligent Battery Backup Units
An intelligent BBU unit 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.
The MegaRAID iBBU units monitor the voltage level of the DRAM modules on MegaRAID controllers. If the voltage
drops below a predefined level, the battery backup module switches the memory power source from the RAID
controller to the battery pack attached to the iBBU unit. As long as the voltage level stays below the predefined value, the
MegaRAID iBBU unit provides power for memory. If the voltage level returns to an acceptable level, the iBBU unit
switches the power source back to the RAID controller, and all pending writes to storage devices are completed with
no data loss.
1.1.3 Intelligent Transportable Battery Backup Units
An intelligent transportable BBU unit, which combines a battery and memory, can be used to move cached data from
a failed controller to a replacement controller. This action could be necessary if, for example, the controller fails after
an unexpected power failure. After you install the iTBBU unit on a new RAID controller of the same type as the failed