Batteries

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 an internal battery to provide power to destage cache and state data to its boot drive, before performing an orderly shutdown.

The battery has enough charge capacity to handle two back-to-back power failures. This means that normally the node canister can restart I/O operations immediately after repowering without waiting to recharge the battery, or requiring any operator intervention. If several power events occur in close succession such that the battery does not have enough charge for the node to save its internal state, the node remains in service until the battery is charged sufficiently.

The battery subsystem supports a one-second ride-through capability to handle a brief AC power outage. During this time, the battery powers the node that continues to run normally servicing host I/O requests. If AC power is restored within the ride-through period, the node continues to run and does not shut down. If AC power does not return within the ride-through period, then the node stops servicing I/O and proceeds to save state data and shut down. When started, the shutdown operations run to completion even if the system power is restored during this time.

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.

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.

Battery management

As a battery ages, it loses capacity. The battery in the node canister lasts at least five years before it cannot hold enough charge to support a successful node shutdown.

The battery management system automatically performs conditioning cycles approximately every three months to ensure accurate determination of their state of health.

When the battery capacity starts to degrade, the system posts an “EOL Warning” event. At this point, the battery subsystem still has enough capacity to be able to support an unscheduled system power-down. If a battery reports an "EOL Warning" event, replace it within approximately six months post the event.

When a battery no longer has capacity to protect against a power loss event, it reports the “EOL Fatal” event. If a battery reports an "EOL Fatal" event, the node goes offline and the battery needs replacing to allow the node to exit from Service state and come online.

If a node canister’s battery fails, that canister goes offline and reports a node error. The remaining canister destages its cache and runs the I/O group in “write-through” mode until its partner canister is repaired and online.

The battery is contained within the node canister, which must be removed from the system to replace the battery.

The node canister has a battery status LED, which is described in Node canister indicators.

To access information about the battery in the management GUI, select Monitoring > System Hardware. On the System Hardware - Overview page, select Battery Module to display information about the battery module.