Battery operation for control enclosures

Each node canister in the control enclosure caches critical data and holds state information in volatile memory.

If the power fails, cache and state data is written to a local flash drive in the canister. The battery within each node canister provides the power to save the critical data and state information.

Note: Expansion canisters do not cache volume data or store state information in volatile memory. Therefore, expansion canisters do not require battery power. If AC power to both power supplies in an expansion enclosure fails, the enclosure powers off. When AC power is restored to at least one power supply, the expansion enclosure restarts without operator intervention.

The battery is maintained in a fully charged state by the battery subsystem. At maximum power, the battery can save critical data and state information in two back-to-back power failures. If power to a node canister is lost, saving critical data starts immediately. The node canister stops handling I/O requests from the host applications. The saving of critical data runs to completion, even if power is restored during this time. The loss of power might be because the input power to the enclosure is lost, or because the node canister is removed from the enclosure.

When the power is restored to the node canister, the system restarts without operator intervention. How quickly it restarts depends on whether there is a history of previous power failures. The system restarts only when the battery has sufficient charge to power the node canister while it saves the critical data again. A node canister with multiple power failures might not have sufficient battery to save critical data. In such a case, the system starts in service state and waits to start I/O operations until the battery has sufficient charge.

Other conditions can cause critical data to be saved and the nodes to go into service state and stop I/O operations. Each node canister saves critical data if it detects there is no longer sufficient battery charge to support saving critical data. Data protection is not guaranteed in this case. The nodes use AC power to save critical data in such a situation and enter service state. The nodes do not handle I/O operations until the remaining battery has sufficient charge to support the saving of critical data.The node canister uses the power that the chassis supplies to save the critical data and then enters service state. The node canister does not handle I/O operations until the battery has sufficient charge to support the saving of critical data. When the battery has sufficient charge, the system automatically restarts.

The node canister has three LEDs indicators that indicate the state of the battery. See "Procedure: Understanding the system status by using the LEDs" for a complete description of the battery LEDs.

In Use
Status
Fault

Important: Although the node canister is resilient to power failures and brown outs, always install in an environment with reliable, consistent, and required AC power. Consider uninterruptible power supply units to avoid extended interruptions to data access.

Design parameters

Consider the following important design parameters:

The design life of the battery in the system is five years service after one year on the shelf.
No periodic learning mode or reconditioning cycle occurs in the battery of this product.
Each battery provides power only for the canister in which it is installed. If a battery fails, the canister goes offline and reports a node error. The single running canister destages its cache and runs the I/O group in "write-through" mode until its partner is repaired and online.