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Chapter 3. RAS and manageability 81
3.1.5 N+1 redundancy
The use of redundant parts allows the p5-520 and p5-520Q to remain operational with full
resources:
Redundant spare memory bits in L1, L2, L3, and main memory
Redundant fans
Redundant power supplies (optional)
3.1.6 Fault masking
If corrections and retries succeed and do not exceed threshold limits, the system remains
operational with full resources, and no intervention is required:
CEC bus retry and recovery
PCI-X bus recovery
ECC Chipkill soft error
3.1.7 Resource deallocation
If recoverable errors exceed threshold limits, resources can be deallocated with the system
remaining operational, allowing deferred maintenance at a convenient time.
Dynamic or persistent deallocation
Dynamic deallocation of potentially failing components is nondisruptive, allowing the system
to continue to run. Persistent deallocation occurs when a failed component is detected, which
is then deactivated at a subsequent reboot.
Dynamic deallocation functions include:
Processor
L3 cache line delete
Partial L2 cache deallocation
PCI-X bus and slots
For dynamic processor deallocation, the service processor performs a predictive failure
analysis based on any recoverable processor errors that have been recorded. If these
transient errors exceed a defined threshold, the event is logged and the processor is
deallocated from the system while the operating system continues to run. This feature
(named
CPU Guard) enables maintenance to be deferred until a suitable time. Processor
deallocation can only occur if there are sufficient functional processors (at least two).
To verify whether CPU Guard has been enabled, run the following command:
lsattr -El sys0 | grep cpuguard
If enabled, the output is similar to the following:
cpuguard enable CPU Guard True
Note: With this optional feature, every deskside or rack-mounted p5-520 or p5-520Q
requires two power cords, which are not included in the base order. For maximum avail-
ability, we highly recommend that you connect power cords from the same p5-520 or
p5-520Q to two separate PDUs in the rack, which are connected to two independent client
power sources. For a deskside p5-520 or p5-520Q, you need to plug power cords to two
independent power sources in order to achieve maximum availability.