Specifications
Chapter 2. Architecture and technical overview 59
2.3.4 Active Memory Mirroring
Power 770 and Power 780 servers have the ability to provide mirroring of the hypervisor
code among different memory DIMMs. This feature will enhance the availability of a server
and keep it operable in case a DIMM failure occurs in one of the DIMMs that hold the
hypervisor code.
The hypervisor code, which resides on the initial DIMMs (J1A to J8A), will be mirrored on the
same group of DIMMs to allow for more usable memory. Table 2-9 on page 56 shows the
DIMMs involved on the Memory Mirroring operation.
Figure 2-14 shows how Active Memory Mirroring uses different DIMMs.
Figure 2-14 Memory Mirroring among different DIMMs
To enable the Active Memory Mirroring (AMM) feature, the server must have 8x DIMMs of the
same size populated on slots J1A to J8A. It is also mandatory that the server has enough free
memory to accommodate the mirrored memory pages. Active Memory Mirroring is required
and automatically enabled on the Power 780. However, on the Power 770 AMM is optional
and is ordered and enabled via feature #4797.
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
There are components that are not mirrored after they are not vital to the regular server
operations and would require a larger amount of memory to accommodate its data:
Advanced Memory Sharing Pool
Memory used to hold the contents of platform dumps
Note: 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.
POWER7
Processor Chip
MC0
MC1
Hypervisor Data J1A
Hypervisor Data J2A
J3A
J4A
Mirrored Hypervisor Data
J5A
Mirrored Hypervisor Data
J6A
J7A
J8A