Memory technology evolution: an overview of system memory technologies, 9th edition

Figure 7. Advanced ECC
Since each ECC device can correct single-bit errors, Advanced ECC can correct a multi-bit error that occurs
within one DRAM chip. As a result, Advanced ECC gives you protection from device failure (Table 1).
Table 1. Comparison of ECC and Advanced ECC error protection
Error Condition ECC Outcome Advanced ECC Outcome
Single-bit Correct Correct
Double-bit Detect Correct or detect
DRAM failure Detect Correct
Although Advanced ECC provides failure protection, it can reliably correct multi-bit errors only when they
occur within a single DRAM chip. Advanced ECC does not provide failover capability. If there is a memory
failure, you must shut down the system before replacing the memory. The latest generation of HP ProLiant
servers offers several forms of Advanced Memory Protection that provide increased fault tolerance for
applications requiring higher levels of availability.
Memory protection technologies
Advanced ECC corrects memory errors, but it does not give your system failover capability. Replacing a
failed DIMM usually raises your operating costs when you take a server down for unscheduled
maintenance, and the shutdown loses revenues for your business. Three available memory protection
technologies, known as Memory Failure Recovery, give you failover and backup capability:
• Online Spare Memory mode
• Mirrored Memory mode
• Lockstep Memory mode
Online Spare Memory mode
In Online Spare Memory mode, you can designate a populated channel (or branch) as the spare, making it
unavailable for normal use as system memory. If a DIMM in the system channel exceeds a threshold rate of
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