HP Smart Array Controller technology, 4th edition

If it is not possible or desirable to replace the batteries, you have three options to disable write-back cache

and avoid losing critical data:

 Use the ACU to adjust the read-and-write cache ratio to 100 percent read cache.

 Use the ACU to disable the array accelerator for each logical drive, which disables both read-ahead and

write-back cache.

 Replace an existing RAID controller with a newer Smart Array controller model.

NOTE:

If the write cache is off, some write performance degradation may occur.

Flash-backed write cache

HP introduced the flash-backed write-cache (FBWC) system in the fourth quarter of 2009. The FBWC uses

flash devices to retain cache data and super-capacitors (Super-caps) instead of batteries to provide power

during a power loss. A BBWC must provide power during the entire power loss, while a FBWC only needs

to provide power during the time to backup from DRAM to flash. The FBWC offers significant advantages

over the HP Battery-backed write-cache (BBWC) system. Since the FBWC writes the contents of memory to

flash devices, there is no longer a 48-hour battery life limitation, and the data posts to the disk drive on the

next power up.

FBWC architecture

he FBWC DDR2 mini-DIMM cache module is designed for the current 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 consist of the cache module, Super-caps with integrated charger, and a RoC

located on the system board, shown in Figure 1.