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You assert that ECC RAM being necessary for ZFS is just a myth but provide no justification for why that is untrue. Is it not the case that if you don't have E

by ylyn 3mo ago

You assert that ECC RAM being necessary for ZFS is just a myth but provide no justification for why that is untrue. Is it not the case that if you don't have ECC memory, ZFS could end up writing a checksum that does not match the data if you get a bitflip in just the right (wrong) spot?

naturalmovement 3mo ago
> You assert that ECC RAM being necessary for ZFS is just a myth but provide no justification for why that is untrue. ZFS without ECC is no more risky than any other file system / software RAID without ECC. As no one owes you an explanation, it would take you five seconds to Google this and discover: 1. It's been disproven, with one of the original ZFS developers chiming in. 2. The original source of the rumor was a forum post that somehow became canon.
- wpm 3mo ago
  What an incredibly rude comment
- cormorant 3mo ago
  > five seconds to Google this and discover ...(after much longer) that it's a rabbit hole with nuance. https://news.ycombinator.com/item?id=18481910 https://news.ycombinator.com/item?id=18481910
Confiks 3mo ago
Yes, indeed. ECC RAM is better than non-ECC RAM, also for ZFS. The myth, popularized by a notorious thread on the TrueNAS forums [1], is specifically that ZFS requires ECC RAM, and will do worse than other filesystems without it, because scrubbing will multiply a single bitflip into a failed pool. A ZFS core developer says that that isn't the case [2]. Here's some more reasoning [3], also about many other myths. [1] https://www.truenas.com/community/threads/ecc-vs-non-ecc-ram-and-zfs.15449/ https://www.truenas.com/community/threads/ecc-vs-non-ecc-ram... [2] https://news.ycombinator.com/item?id=18480016 https://news.ycombinator.com/item?id=18480016 [3] https://kldload.com/zfs-wiki/myths https://kldload.com/zfs-wiki/myths
- magicalhippo 3mo ago
  Updated link to the post from Matt Ahrens here[1], which is one of the ZFS creators[2] not "just" a core developer. [1]: https://arstechnica.com/civis/threads/ars-walkthrough-using-the-zfs-next-gen-filesystem-on-linux.1235679/post-26303271 https://arstechnica.com/civis/threads/ars-walkthrough-using-... [2]: https://en.wikipedia.org/wiki/ZFS#2004%E2%80%932010:_Development_at_Sun_Microsystems https://en.wikipedia.org/wiki/ZFS#2004%E2%80%932010:_Develop...
- dijit 3mo ago
  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.
  - sgt 3mo ago
    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)
  - layer8 3mo ago
    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 3mo ago
    > 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.
vardalab 3mo ago
Had it happen to my PBS backups running on ZFS without ECC just the other day. Turned out to be heat related, memory was fine but during long backups heat was causing bit flips.

by ylyn 3mo ago

naturalmovement 3mo ago

> You assert that ECC RAM being necessary for ZFS is just a myth but provide no justification for why that is untrue. ZFS without ECC is no more risky than any other file system / software RAID without ECC. As no one owes you an explanation, it would take you five seconds to Google this and discover: 1. It's been disproven, with one of the original ZFS developers chiming in. 2. The original source of the rumor was a forum post that somehow became canon.

wpm 3mo ago
What an incredibly rude comment
cormorant 3mo ago
> five seconds to Google this and discover ...(after much longer) that it's a rabbit hole with nuance. https://news.ycombinator.com/item?id=18481910 https://news.ycombinator.com/item?id=18481910

Confiks 3mo ago

Yes, indeed. ECC RAM is better than non-ECC RAM, also for ZFS. The myth, popularized by a notorious thread on the TrueNAS forums [1], is specifically that ZFS requires ECC RAM, and will do worse than other filesystems without it, because scrubbing will multiply a single bitflip into a failed pool. A ZFS core developer says that that isn't the case [2]. Here's some more reasoning [3], also about many other myths. [1] https://www.truenas.com/community/threads/ecc-vs-non-ecc-ram-and-zfs.15449/ https://www.truenas.com/community/threads/ecc-vs-non-ecc-ram... [2] https://news.ycombinator.com/item?id=18480016 https://news.ycombinator.com/item?id=18480016 [3] https://kldload.com/zfs-wiki/myths https://kldload.com/zfs-wiki/myths

magicalhippo 3mo ago
Updated link to the post from Matt Ahrens here[1], which is one of the ZFS creators[2] not "just" a core developer. [1]: https://arstechnica.com/civis/threads/ars-walkthrough-using-the-zfs-next-gen-filesystem-on-linux.1235679/post-26303271 https://arstechnica.com/civis/threads/ars-walkthrough-using-... [2]: https://en.wikipedia.org/wiki/ZFS#2004%E2%80%932010:_Development_at_Sun_Microsystems https://en.wikipedia.org/wiki/ZFS#2004%E2%80%932010:_Develop...
dijit 3mo ago
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.
- sgt 3mo ago
  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)
- layer8 3mo ago
  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 3mo ago
  > 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.

vardalab 3mo ago

Had it happen to my PBS backups running on ZFS without ECC just the other day. Turned out to be heat related, memory was fine but during long backups heat was causing bit flips.