Dell POWERVAULT MD3620I - Manual (Page 34)

34 Planning: RAID Controller Modules
RAID Controller Module—Additional Features
Battery Backup Unit
Each RAID controller contains a two-cell Lithium ion nanopolymer battery
backup unit (BBU). It provides power to the RAID controller module in the
event of a power outage. For information on removing and installing the BBU,
see "RAID Controller Module Backup Battery Unit" on page 232.
NOTE: For virtual disks, the RAID controller firmware changes the data cache
setting based on the state of the battery. If the battery is missing or does not have
sufficient charge, the controller flushes the cache and sets the write cache
attribute to Write Through for all virtual disks. When the battery is replaced, Write
Back is re-enabled.
Storage Array Thermal Shutdown
The system automatically shuts down when the system temperature exceeds
the safe threshold. The battery backup unit protects against data loss by
providing power to offload to non-volatile memory in the event of power loss.
It is not necessary to shut down any MD1200 Series expansion enclosures
attached to the storage array when thermal shutdown occurs.
Temperature threshold values determine the temperature at which shutdown
occurs. These thresholds cannot be changed.
Table 3-1. Shutdown Threshold Type
Threshold Temperature Exceeding Event Description
Nominal failure threshold
A critical event is set
Maximum failure threshold The system power supplies shut down within 3
minutes
Shutdown threshold The system power supplies shut down within 5
seconds
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