Chapter 3. Understanding The Storwize V7000 Battery Operation For The Control Enclosure - IBM Storwize V7000 Troubleshooting And Maintenance Manual

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Chapter 3. Understanding the Storwize V7000 battery
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operation for the control enclosure
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Storwize V7000 node canisters cache volume data and hold state information in volatile memory.
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4 If the power fails, the cache and state data is written to a local solid-state drive (SSD) that is held within
the canister. The batteries within the control enclosure provide the power to write the cache and state
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data to a local drive.
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Note: Storwize V7000 expansion canisters do not cache volume data or store state information in volatile
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4 memory. They, therefore, do not require battery power. If ac power to both power supplies in an
4 expansion enclosure fails, the enclosure powers off. When ac power is restored to at least one of the
power supplies, the controller restarts without operator intervention.
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There are two power supply units in the control enclosure. Each one contains an integrated battery. Both
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power supply units and batteries provide power to both control canisters. Each battery has a sufficient
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4 charge to power both node canisters for the duration of saving critical data to the local drive. In a fully
redundant system with two batteries and two canisters, there is enough charge in the batteries to support
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saving critical data from both canisters to a local drive twice. In a system with a failed battery, there is
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4 enough charge in the remaining battery to support saving critical data from both canisters to a local drive
once.
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4 If the ac power to a control enclosure is lost, the canisters do not start saving critical data to a local drive
until approximately 10 seconds after the loss of ac power is first detected. If the power is restored within
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this period, the system continues to operate. This loss in power is called a brown out. As soon as the
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4 saving of the critical data starts, the system stops handling I/O requests from the host applications, and
Metro Mirror and Global Mirror relationships go offline. The system powers off when the saving of the
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critical data completes.
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If both node canisters shut down without writing the cache and state data to the local drive, the system
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is unable to restart without an extended service action. The system configuration must be restored. If any
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4 cache write data is lost, volumes must be restored from a backup. It is, therefore, important not to
remove the canisters or the power supply units from the control enclosures unless directed to do so by
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4 the service procedures. Removing either of these components might prevent the node canister from
4 writing its cache and state data to the local drive.
4 When the ac power is restored to the control enclosure, the system restarts without operator intervention.
How quickly it restarts depends on whether there is a history of previous power failures.
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4 When the ac power is restored following a power outage that causes both canisters to save their critical
data, the system restarts only when the batteries have sufficient charge to power both canisters for the
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duration of saving the critical data again. In a fully redundant system with two batteries, this condition
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4 means that after one ac power outage and a saving of critical data, the system can restart as soon as the
power is restored. If a second ac power outage occurs before the batteries have completed charging, then
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the system starts in service state and does not permit I/O operations to be restarted until the batteries are
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4 half charged. The recharging takes approximately 30 minutes.
In a system with a failed battery, an ac power failure causes both canisters to save critical data and
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4 completely discharges the remaining battery. When the ac power is restored, the system starts in service
state and does not permit I/O operations to be restarted until the remaining battery is fully charged. The
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recharging takes approximately 1 hour.
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© Copyright IBM Corp. 2010
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