Battery backup unit

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A battery backup unit (BBU), some manufacturers also known as battery backup modules or Battery Backup Write Cache Enabler called (BBWC), supplies battery supported the cache of a RAID controller in a power failure briefly with energy. In addition to an uninterruptible power supply (UPS), it guarantees the highest level of data and failure security .

Due to the continued power supply, the content of the cache is typically retained for up to 72 hours, depending on the state of the battery. The maximum duration depends on the capacity of the BBU battery. Modern BBUs have a number of modes with which the service life of the battery or the autonomy time can be optimized depending on the environment.

Unlike a UPS a BBU is not between the power supply of the server connected and the outlet, but is mounted directly on the controller and thus independent of the power supply. The batteries in the BBU are charged via the mains power during normal operation. In contrast to the UPS, a BBU protects the cache contents of a RAID controller even if the server's power supply unit is damaged. However, it is necessary to restore the normal power supply as soon as possible, because after a while the battery will be empty and the contents of the cache would then be lost, especially if the write cache is activated for the database server.

As the capacity of the battery decreases over time, it must be checked regularly and replaced if necessary.

Alternatively, solutions using NAND flash memories and capacitors are also offered. Such a Maintenance Free Backup Unit (MFBU) copies the controller's cache to the non-volatile NAND flash in the event of an error. The capacitors provide the energy to end the copying process even without a power supply.

See also

RAID: cache controller with backup battery

Individual evidence

  1. ↑ Intel® RAID Backup (Batteries / Flash) (Intel)
  2. ↑ Maintenance of the Battery Backup Unit (BBU / BBM) for RAID controllers (Thomas Krenn Wiki)
  3. ↑ The differences between BBU and MFBU (Servermeile Technet - The Knowledge Database)