IBM Power 780 Technical Overview And Introduction page 185

Mirroring optimization
Hypervisor mirroring requires specific memory locations. Those locations might be assign to
other purposes (for LPAR memory, for example) because of memory's management based on
the logical memory block. To "reclaim" those memory locations, an Optimization Tool is
available on the Advanced tab of the system properties (Figure 4-6).
Figure 4-6 Optimization Tool
You can define the amount of memory available for mirroring by either selecting a custom
value or making available as much mirrorable memory as possible. After selecting OK, this
action copies the active partition's contents from one LMB to another to free the pairs of
mirrored memory. The copy operation will have a slight impact on performance while in
progress.
The operation can be stopped by selecting Cancel. A time limit can also be specified.
DIMM guard at system boot
During system boot, the FSP will guard a failing DIMM. Because there will not be eight
functional DIMMs behind a memory controller, hypervisor mirroring is not possible on this
chip. Then at boot time, the following events occur:
If there are other chips in the book with mirrorable memory, the system will boot
fully mirrored.
If this was the only mirrorable memory in this book, hypervisor enters a partially mirrored
state. Not all of the hypervisor objects are mirrored, and therefore are unprotected.
Hypervisor will continue to mirror as much as possible to continue to provide protection. If
a second uncorrectable error occurs in the same CEC while in partial mirror state, this will
likely result in system failure. The system remains partially mirrored until the DIMM is
replaced and the CEC is rebooted.
Chapter 4. Continuous availability and manageability
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