alt Hacker News>> Everyone repeats the statement DDR5 on-die ECC isn’t a replacement for regular ECC, but nobody ever shows data on DDR5 bitflips.
That's because the on-die ECC cannot detect errors in the transmission of data from the DIMMs to the CPU. It seems like on-die ECC is meant to "hide" some level of errors to make less reliable RAM chips appear good. I have no idea if that's a reasonable way to do it, but it seems like it could be misused. Like TFA suggests, we need to know how the two levels of ECC interact.
Right. Everyone agrees that real ECC is more robust, and production servers of course run it. But it seems to me that if most RAM bitflips are in the module itself (rather than in transmission to CPU), then on-die ECC could in theory make the probability of a bitflip in practice so low that for things like home servers it isn’t worth the price premium for real ECC. But without data on this, everyone is just speculating.