Hitachi Compute Rack CR 210H User Manual page 48

The precautions on use of lock step are as follows:
To validate the lock step function, set Chipset > North Bridge > Memory

Mode to Lock Step on the system BIOS setup menu.
Interleave between channels is not performed, so the memory access

performance becomes lower than independent mode.
In case of a correctable memory error, such as a 1-bit error or single DRAM

chip error, automatic correction is continued. At this time, the ERROR LED
does not turned on.
If an uncorrectable memory error occurs, ECC-based error correction

becomes unavailable and thus the system is shut down.
You cannot use the lock step function simultaneously with online spare

memory, memory mirroring, and device tagging.
Device tagging
Memory device tagging is a function for providing redundancy on a DRAM chip
basis so that the system can operate without a shutdown even if one DRAM chip
on a memory board breaks down.
Normally, memory generates an ECC from data and stores on each DRAM chip
separately from data.
If the entire single DRAM chip fails, the data stored on the failed DRAM chip is
calculated according to the data and ECC stored on other DRAM chips in order to
rewrite the data on the DRAM chip storing ECC. This can avoid an uncorrectable
memory error caused by a multi-bit error.
Figure 3-19: The function of device tagging
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System Unit Functions
Hitachi Compute Rack 210H User's Guide
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ECC
Data