HP ProLiant SE2170s Memory technology evolution: an overview of system memory - Page 10

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 Single-bit Double-bit DRAM failure ECC Outcome Correct Detect Detect Advanced ECC Outcome Correct Correct or 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 10