Chapter 2. Architecture and technical overview 57
It is possible to check whether the Active Memory Mirroring option is enabled and change its
current status through HMC, under the Advanced Tab on the CEC Properties panel
(Figure 2-10).
Figure 2-10 CEC Properties panel on an HMC
After a failure on one of the DIMMs containing hypervisor data occurs, all the server
operations remain active and flexible service processor (FSP) will isolate the failing DIMMs.
Because there are no longer eight functional DIMMs behind a memory controller, Active
Memory Mirroring are not available until this DIMM is replaced. Systems stay in the partially
mirrored state until the failing DIMM is replaced.
There are components that are not mirrored because they are not vital to the regular server
operations and require a larger amount of memory to accommodate its data:
Advanced Memory Sharing Pool
Memory used to hold the contents of platform dumps
With AMM, uncorrectable errors in data that are owned by a partition or application are
handled by the existing Special Uncorrectable Error handling methods in the hardware,
firmware, and operating system.
2.3.6 Special Uncorrectable Error handling
Special Uncorrectable Error (SUE) handling prevents an uncorrectable error in memory or
cache from immediately causing the system to terminate. Rather, the system tags the data
and determines whether it will ever be used again. If the error is irrelevant, it does not force a
checkstop. If the data is used, termination can be limited to the program/kernel or hypervisor
owning the data, or freeze of the I/O adapters controlled by an I/O hub controller if data is to
be transferred to an I/O device.
Partition data: Active Memory Mirroring will not mirror partition data. It was designed to
mirror only the hypervisor code and its components, allowing this data to be protected
against a DIMM failure
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