ISS Technology Update, Volume 9, Number 2

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Smart Array flash-backed write-cache
The HP flash-backed write-cache (FBWC) system offers important advantages over battery-backed write-cache (BBWC)
systems. HP designed the FBWC with NAND
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flash devices so that power is not required to retain cache data. There is no
longer a 48-hour battery life limitation and the data will be posted to the disk drive the next time you power up the server.
HP has engineered the FBWC to function with long-life super-capacitors (Super-caps) instead of a battery. The Super-cap is
only used to power the FBWC system during data backup. The result is that the FBWC retains cache data regardless of
server power states and you can adjust maintenance and replacement schedules to accommodate the longer Super-cap
lifecycle. Figure 1-1 displays the FBWC module and the Super-cap housing.
Figure 1-1. HP flash-backed write-cache and Super-cap power supply housing
NOTE:
The Super-cap is a capacitor, not a battery. The Super-cap module is contained within the same form factor and
housing as the HP-650 mAh P-Series battery used in the HP BBWC. The NAND flash devices do not require
sustained power to retain data. However, if server power fails, the FBWC does require power from the Super-cap
to copy data contained in the DRAM to the flash devices. Always install the Super Cap module with the FBWC.
FBWC architecture
The FBWC DDR2 mini-DIMM cache module is specifically designed for the present generation of PCIe2.0, SAS-based Smart
Array controllers based on the PMC PM8011 max SAS SRC 8x6G RAID on a chip (RoC). The primary FBWC components
are the cache module, Super-caps with integrated charger, and a RoC located on the system board, shown in Figure 1-2.
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Non-volatile semiconductor memory that can be electronically erased and reprogrammed. No power is needed to maintain data stored in the chip