BBU Overview

Each canister contains a Battery Backup Unit (BBU) that is used to power just that canister when the AC power fails.

BBU Operation

The goal of the BBU is: during an AC power loss, the BBU can power the system long enough to complete a data dump.

• Power the canister for five seconds of ride-through (meaning the OS and application SW continues to run on the canister even though the drives have dropped offline) and can quickly recover/continue should power return.

• Power the canister for an additional one second transition time where the application SW realizes that the power is not coming back. The application SW needs to terminate any activities on the PCIe buses and then signal back to the CPLD that it is now safe to power down all the PCIe devices and IO cards. The CPUs should also be forced into a lower power state by decreasing the operation frequency.

• CPLD will then remove power from unnecessary PCIe devices and PCIe cards to reduce power load on the BBU.

• Application SW should then start an operation to save any critical data from the DIMM memory into one or both of the M.2 SSDs located on the canister. BBU power is expected to last about 300 seconds in this mode. After that time, the application SW should signal to the CPLD that it has completed, which allows the CPLD to power down the canister completely until AC power returns. BBU will continue to discharge if the system has not been powered down even when the dump is completed.

Assuming a write speed of ~1000MB/s of a PCIe based M.2 card, we estimate that the 180 second data save time should allow for backup saving of ~180GB of data if one of the M.2 SSDs is used, and twice that ~360GB of data if both M.2 SSDs are used in parallel. If faster M.2 modules are used, then more data can be saved.

Testing will be needed on specific configurations as both the behavior of the M.2 SSDs and the Intel® C620 Series Chipset can affect the transfer speeds and total backup time.

BBU Design

The BBU consists of 6 Sony VTC5 (2600ma-hr) cells 18650 format arranged in a 2-Parallel/ 3-Series (2P3S) arrangement.

It is designed to deliver ~410W for 6 seconds, followed by 205W for 180 seconds.

Nominal Output Voltage: 10.8V, Cutoff Voltage: 7.5V, the output voltage we decrease with charge level.

When new, the battery pack has ~58.3W-hr of energy, which is below the 100W-hr limit to ship the packs by air.