Battery operation for control enclosures

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

If power to a node canister fails, the node canister uses battery power to write cache and state data to its boot drive.
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 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 after a five-second wait. (If the outage is shorter than five seconds, the battery continues to support the node and critical data is not saved.) The node canister stops handling I/O requests from 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 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 for the node canister to save the cache and state data again. A node canister with multiple power failures might not have sufficient charge 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.

Two light-emitting diode (LED) indicators indicate the state of the battery:
  • Status LED - Green
  • Fault LED - Amber

See Procedure: Understanding the system status using the LEDs for information about the battery LEDs. For more information about the batteries, see Replacing the battery in a node canister and.Removing and replacing the node canister battery.

Important: Although the system is resilient to power failures and brown outs, always install the enclosures in an environment that has 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 control enclosure is five years service after one year on the shelf.
  • Each battery is automatically reconditioned every three months to measure the battery capacity. Batteries in the same enclosure are not reconditioned within two days of each other. If a battery has a lower capacity than required (below the planned threshold), it is marked as End Of Life and should be replaced.
  • 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 canister is repaired and online.