Hardware options installation 43
Advanced ECC provides additional protection over Standard ECC because it is possible to correct certain
memory errors that would otherwise be uncorrected and result in a server failure. The server provides
notification that correctable error events have exceeded a pre-defined threshold rate.
Mirrored memory configuration
Mirroring provides protection against uncorrected memory errors that would otherwise result in server
downtime. Mirroring is performed at the channel level. Channels 1 and 2 are used; channel 3 is not
populated.
Data is written to both memory channels. Data is read from one of the two memory channels. If an
uncorrectable error is detected in the active memory channel, data is retrieved from the mirror channel.
This channel becomes the new active channel, and the system disables the channel with the failed DIMM.
Online Spare memory configuration
Online spare memory provides protection against degraded DIMMs by reducing the likelihood of
uncorrected memory errors. This protection is available without any operating system support.
Online spare memory protection dedicates one rank of each memory channel for use as spare memory.
The remaining ranks are available for OS and application use. If correctable memory errors occur at a
rate higher than a specific threshold on any of the non-spare ranks, the server automatically copies the
memory contents of the degraded rank to the online spare rank. The server then deactivates the failing
rank and automatically switches over to the online spare rank.
Lockstep memory configuration
Lockstep mode provides protection against multi-bit memory errors that occur on the same DRAM device.
Lockstep mode can correct any single DRAM device failure on x4 and x8 DIMM types. The DIMMs in
each channel must have identical HP part numbers.
Lockstep mode uses channel 1 and channel 2. Channel 3 is not populated. Because channel 3 cannot be
populated when using Lockstep mode, the maximum memory capacity is lower than Advanced ECC
mode. Memory performance with Advanced ECC is also slightly higher.
General DIMM slot population guidelines
Observe the following guidelines for all AMP modes:
• Populate DIMM slots for a processor only if the processor is installed.
• To maximize performance in multi-processor configurations, distribute the total memory capacity
between all processors as evenly as possible.
• Do not mix Unbuffered and Registered PC3 DIMMs.
• Each channel supports up to two Unbuffered DIMMs.
• If quad-rank DIMMs are installed for a processor, a maximum of two DIMMs can be installed on
each channel for that processor.
• If a channel contains quad-rank DIMMs, the quad-rank DIMM must be installed first on that channel.
DIMM speeds are supported as indicated in the following table.
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