Intel® RAID Modules RMSP3AD160F, RMSP3CD080F and RMSP3HD080E Hardware User Guide
38
7.
Intel® RAID Maintenance Free Backup Unit AXXRMFBU7
(RMFBU)
7.1
Intel® RAID Maintenance Free Backup Unit AXXRMFBU7
Intel® RAID Modules and Intel® RAID Adapters provide reliability, high performance, and fault-tolerant disk
subsystem management. A complete fault-tolerant strategy requires protection of all data, including the
unwritten cached data in the RAID card’s RAM cache. If power is lost, the data in the RAM cache is lost. To avoid
losing this data, a RAID Maintenance Free Backup Unit (RMFBU) can be added to the configuration.
During normal system operation, the RMFBU monitors the voltage level of the DRAM of the Intel® RAID Module
or Intel® RAID Module. If the voltage drops below a predefined level due to an AC power failure or brief power
outage, the RMFBU protects the integrity of the cached data by providing sufficient back-up power to offload
the data from the RAID RAM to the NAND flash. When the voltage level returns to an acceptable level, the RAID
RAM is recovered from flash, and all pending writes to storage devices are completed without losing any data.
The cache memory available on Intel® RAID Modules and Intel® RAID Adapters can improve the overall system
performance. Writing data to the module’s cache memory is much faster than writing data to a storage device.
Write operations appear to complete very quickly at the software application level. The Intel® RAID Module
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 is written to the
storage device. This risk factor is eliminated when the Intel® RAID Module has an RMFBU installed. In addition,
the RMFBU provides an alternative to using an Uninterruptible Power Supply (UPS) or can act as a second level
of fault tolerance when used with a UPS. Furthermore, it eliminates the need for lithium ion (Li-ion) batteries
traditionally used to protect DRAM cache memory on PCI RAID modules. Therefore this is a greener and lower
total cost cache protection solution.
The RMFBU has built-in functionality to charge the capacitor module automatically and to communicate status
information such as voltage, temperature, and current to the host server system.
The AXXRMFBU7 RMFBU is a kit consisting of a FBU345 super capacitor bank, a plastic bracket to attach the
super capacitor bank to the chassis, and two (2) extender cables, one 605 mm long and the other 930 mm
long. The FBU345 consists of a bank of Electric Double-Layer Capacitors (EDLC) or super capacitors capable
of storing a high amount of electric energy while active. In the event of a power failure, the FBU345 provides
the power needed for the data offload. It also has an over-temperature detection circuitry and a discharge
circuitry that discharges the capacitors while disconnected from the RAID module or when the system on which
it is installed is turned off.
