To shut the system down in an emergency, power off the controller first, then
the drive units, as follows.
1. Open the back door of the rack that contains the control unit.
a. Turn off the circuit breakers in both lower PDUs in the rack.
b. Turn off the circuit breakers in both upper PDUs in the racks with the
control unit.
2. Open the back doors of all racks that contain only drive units and turn the
circuit breakers off in all the PDUs in any order in those racks.
Power on procedure after emergency power off
To power up the HUS VM storage system after emergency shutdown, reverse
the emergency power off procedure.
1. In all system racks, turn on the circuit breakers in the PDUs that power
the drive units.
2. In the controller rack, turn on the circuit breakers in the PDUs that power
the controller.
3. Follow the instructions in
Normal Power on/off procedures on page 5-4.
Battery backup operations
The HUS VM is designed so that it cannot lose data or configuration
information if the power fails. The battery system is designed to provide
enough power to completely destage all data in the cache if two consecutive
power failures occur and the batteries are fully charged. If the batteries do
not contain enough charge to provide sufficient time to destage the cache
when a power failure occurs, the cache operates in write through mode. This
synchronously writes to HDDs to prevent slow data throughput in the cache.
When the battery charge is 50% or more, the cache write protect mode
operates normally.
When a power failure occurs and continues for 20 milliseconds or less, the
storage system continues normal operation. If the power failure exceeds 20
milliseconds, the storage system uses power from the batteries to back up
the cache memory data and storage system configuration data to the cache
flash memory on each cache board. This continues for up to ten minutes. The
flash memory does not require power to retain the data.
The following illustration shows the timing in the event of a power failure.
5-6
Power On/Off procedures
Hitachi Unified Storage VM Block Module Hardware User Guide
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