IBM Storwize V7000 Unified Problem Determination Manual page 261

When ac power is restored after both canisters save critical data, 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
batteries have sufficient charge to save critical data for both node canisters again. A
fully redundant system can restart as soon as power is restored after it saves
critical data once. If a second ac power outage occurs before batteries charge
completely, the system starts in service state. The system does not begin I/O
operations until the batteries are half charged. Recharging takes approximately 30
minutes.
In a system with a failed battery, an ac power failure causes both canisters to save
critical data and completely discharges the remaining battery. When the ac power
is restored, the system starts in service state and does not start I/O operations
until the remaining battery is fully charged. The recharging takes approximately 1
hour.
A battery is considered failed for the following conditions:
v The system can communicate with the battery, but the battery reports an error.
v The system is unable to communicate with the battery. The failure exists because
the power supply is absent or because the power supply failed without
communicating with the system.
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.
This situation happens, for example, when both batteries have two-thirds of a
charge. The total charge is sufficient to support saving critical data once. Therefore,
both canisters are in active state and I/O operations occur. If one battery fails, the
remaining battery has only two-thirds of a charge. The total charge in the enclosure
is now insufficient to save critical data if the ac power fails. 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. When
the battery has sufficient charge, the system automatically restarts.
Important: Although Storwize V7000 Unified 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:
v The design life of the battery in the Storwize V7000 Unified is five years service
after one year on the shelf.
v No periodic learning mode or reconditioning cycle occurs in the battery of this
product.
v 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.
Chapter 5. Control enclosure
233