The batteries temporarily provide the storage system with power to maintain its caching operation during a power failure event. The following information describes the battery life expectancy, battery operation, and cache backup process. Also, some specific guidelines are provided for storing the system during an extended period of time non-operation.
Battery backup operations
The storage system is designed to retain data and configuration information when the power fails. The battery system can provide sufficient power with fully charged batteries to completely back up all data in the cache if two consecutive power failures occur. If the batteries do not contain enough charge to provide sufficient time to back up the cache when a power failure occurs, the cache operates in write-through mode and writes directly to the drives to prevent slow data throughput via the cache. When the battery charge is 50% or more, the cache write through mode is turned off and the system operates normally.
If a power failure occurs and continues for up to 20 milliseconds, the storage system continues normal operation. If the power failure exceeds 20 milliseconds, the storage system uses power from the batteries to keep the cache active while the system copies the storage system configuration and cached data to the cache flash memory in the cache backup modules. The process continues up to 32 minutes. The cache flash drives do not require power to retain the data.
The following illustration shows the timing if a power failure occurs.
Power failure occurs.
The storage system continues to operate for 20 milliseconds and detects the power failure.
The cache memory data and storage system configuration are backed up to the cache flash memory in the cache backup assemblies. If power is restored during the backup, the backup stops unless the backup battery capacities are used less than 50%. In case, the system operates in write-through mode until the batteries are charged enough for a full backup.
Data is stored in the cache flash memory until power is restored, and then it is written to the drives.
Cache backup batteries
If a power failure occurs, nickel-hydride batteries keep the cache memory active while the entire storage system configuration and data in the cache are copied to the flash memory in the cache backup modules. The batteries are located in the cache backup modules. They are fully charged at the distribution center where the storage system is assembled and tested. During shipment, the batteries are disconnected automatically to prevent any discharging during shipping and storage until the system is installed. During installation, they are reconnected. The following figure provides an overview of the cache backup battery.
The batteries have a lifespan of three years and hold a charge for a specific amount time when disconnected. When the batteries are connected and power is on, the batteries are continuously charging. The process occurs during both normal system operation and while the system is in idle mode.
When the batteries are connected and the power is off, the batteries slowly discharge its power. The batteries have a charge of less than 50% after two weeks without power. When the batteries are fully discharged, the batteries must be connected to power for three hours to fully recharge.
Storing the system
While connected, the cache backup batteries completely discharge in two to three weeks without power. If you are not using the storage system for two weeks or more, contact customer support to move the batteries to an active storage system, or set the storage system to idle mode for at least 3 hours once every two weeks.
If you store the system for more than two weeks without disconnecting the cache backup batteries, the batteries need to charge for at least 90 minutes when you restart the system before the cache can be protected. To prevent the batteries from discharging during long-term storage, contact technical support and request a disconnection of the battery jumpers on the cache boards.