3Com Switch 4007R Getting Started Manual page 51

Rather, a factory-defined power limit (which is
based on the number of installed power supplies)
ensures that power that is equivalent to at least
one power supply is available to replace power
that is lost when a power supply fails.
The amount of power that installed modules in a
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chassis require must not be greater than the
number of installed power supplies, minus one
(n-1). When you reserve power that is equivalent
to one power supply in power fault-tolerant mode,
the failure of a single power supply has no impact
on installed modules that are already powered on.
If a power supply fails while the Switch is running in
power fault-tolerant mode:
EMEs respond by automatically disabling power
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fault-tolerant mode.
Power formerly reserved (unavailable to installed
I
modules) is made available by power class and slot
location to power-enabled Switch 4007R modules
to prevent them from powering off (as an attempt
to bring power consumption under the
now-reduced power budget).
All modules that had power before the power
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supply failure continue to receive power without
interruption.
Upon power supply recovery, the EME
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automatically reenables power fault-tolerant
mode.
Operate the Switch 4007R in power fault-tolerant
mode to ensure that power that is equivalent to at
Power Supply Modes
least one power supply is available to replace power
that is lost if a single power supply fails.
To set the Switch 4007R to power fault-tolerant mode
or to power non-fault-tolerant mode, enter the
command at the EME prompt.
power mode
When you attempt to set the Switch 4007R to power
fault-tolerant mode, EMEs determine if there is
sufficient unallocated power budget available to place
power that is equivalent to one power supply in
reserve.
If there is sufficient unallocated power budget, the
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Switch 4007R sets to power fault-tolerant mode.
If there is insufficient unallocated power budget,
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the Switch 4007R remains in power
non-fault-tolerant mode.
To prevent management modules from automatically
disabling power fault-tolerant mode in response to a
power supply failure, ensure that the number of
installed power supplies is equal to or greater
than n-2 (two extra power supplies). In a Switch
4007R with at least two extra installed power
supplies, n-1 power supplies continue to be available
to run the system in power fault-tolerant mode, even
after a single power supply fails.
If a power supply failure occurs under any condition,
an alert is sent to the management application.
Non-fault tolerant mode — A user-selectable mode
in which 100 percent of the power that can be
allocated to all modules is available to them (no
power is held in reserve). This is the default mode for
power supplies as shipped.
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set