Chapter 2. Architecture and technical overview
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Active Memory Mirroring (AMM) is included with all Power E870 and Power E880 systems at
no additional charge. It can be enabled, disabled, or re-enabled depending on the user’s
requirements.
The hypervisor code logical memory blocks will be mirrored on distinct CDIMMs to allow for
more usable memory. There is no specific CDIMM that hosts the hypervisor memory blocks
so the mirroring is done at the logical memory block level, not at the CDIMM level. To enable
the AMM feature it is mandatory that the server has enough free memory to accommodate
the mirrored memory blocks.
Besides the hypervisor code itself, other components that are vital to the server operation are
also mirrored:
Hardware page tables (HPTs), responsible for tracking the state of the memory pages
assigned to partitions
Translation control entities (TCEs), responsible for providing I/O buffers for the
partition’s communications
Memory used by the hypervisor to maintain partition configuration, I/O states, virtual I/O
information, and partition state
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 2-16).
Figure 2-16 CEC Properties panel on an HMC
After a failure on one of the CDIMMs containing hypervisor data occurs, all the server
operations remain active and flexible service processor (FSP) will isolate the failing CDIMMs.
Systems stay in the partially mirrored state until the failing CDIMM 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
