[dijit]

Usually if you’re using a NAS you don’t want to lose data, ZFS is not significantly more sensitive than everything else.

But everything is actually quite sensitive.

We’ve accepted lack of ECC because Intel decided it would be a product line differentiator, and serious customers who didn’t want random crashes or to lose data would buy chips with ECC.

It’s actually less of an issue these days because DDR5 has (by spec) some in-line ECC; won’t help with multi-bit errors but its an improvement on what came before.

[layer8]

DDR5 on-die ECC is to achieve acceptable yields in the face of denser process nodes that decrease the reliability of RAM cells. It’s not clear how much of an improvement that is to what we had before, other than allowing for higher RAM speeds. It doesn’t replace side-band ECC.

[toast0]

> We’ve accepted lack of ECC because Intel decided it would be a product line differentiator, and serious customers who didn’t want random crashes or to lose data would buy chips with ECC.

AMD has been allowing ECC on lots of regular hardware for a long time.

People don't tend to buy ECC for desktop use because it costs significantly more (used server ram is/was often cheap... but it often doesn't work in desktop boards), and the performance specs are poor.

My home servers are mostly retired desktops, so they get my old desktop ram and I don't want to pay premium prices for jedec speed ecc ram on my desktops, thanks.

Since DDR5 doesn't include reporting on bit errors (afaik), it likely means much fewer single bit errors, but most experienced errors will be multi-bit. Although, I dunno what proportion of bit errors is on the ram chips and what's on the bus... there's no protection from bus errors.

If there were reporting, you could replace chips with high error rates, but without reporting you'll keep running them until they fail enough to notice.

[Dylan16807]

> AMD has been allowing ECC on lots of regular hardware for a long time.

Often unsupported or untested by the motherboard manufacturer, because the precedent set quite a while ago has stood so strongly.

> because it costs significantly more [...] and the performance specs are poor

Because it's niche. If a large share of the desktop market was using ECC memory, the extra cost would have been 10-12%, and a typical kit would push the clocks and timings at least as much as non-ECC memory.

> Since DDR5 doesn't include reporting on bit errors (afaik), it likely means much fewer single bit errors, but most experienced errors will be multi-bit. Although, I dunno what proportion of bit errors is on the ram chips and what's on the bus... there's no protection from bus errors.

Yeah that sucks. I'm really hoping that DDR6 standardizes a light form of end to end ECC. (Bursts are 24 bits wide and 24 bits deep, so on top of the 512 bits of payload there's a bunch of extra bits that can be used for ECC. If memory chips would just store 4 extra bits per 128, that's enough for reasonable ECC on a per-burst basis.)

[toast0]

> the precedent set quite a while ago has stood so strongly.

I wasn't really around for it, but I appreciate the early penny pinchers that developed fake parity ram. The IBM PC required a parity bit per byte?, but you could add an xor chip to calculate it at read and save out on the expensive ram chip.

I wouldn't mind paying a little more for ECC, what with the extra chip and a little more circuitry, but desktop ECC often starts at 50% more, which I'm way too cheap to pay for.

[Dylan16807]

My favorite parity trick was how the N64 was designed around ECC RAM chips but didn't bother using ECC, so it has a ninth bit at every address that the CPU ignores and the GPU uses as extra storage.

[sgt]

I know that LPDDR5 has ECC, and not just single bit AFAIK, but if you enable it you lose some memory capacity (the 128 bit bus minus 16 bit for ECC error correction, making it effectively 112 bits)