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I've been reading up on FreeNAS and RAID Z, and one of the things people kept mentioning is that you shouldn't use ZFS (or more specifically, RAID Z) on a machine without ECC RAM. I'm wondering what the reasoning behind this is. Is this an issue with RAID Z specifically? Is there any particularly heightened risk from not using ECC RAM with ZFS vs other file systems? Or is this just a general concern about corrupt memory spreading to a filesystem which would otherwise have corrected the error thanks to its support for self-healing redundant arrays?

Ajedi32
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  • Why the downvote by the way? If there's anything in particular about this post which needs improvement, please let me know. Or was it more of a "you don't know enough about ECC RAM to formulate a good question on this topic" sort of thing? – Ajedi32 Mar 05 '15 at 02:46
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    ZFS requires a lot of RAM, so it does make sense to protect it from random errors. Just as you should go to RAID/ZFS when you grow data storage, you should move to ECC when system actively uses a lot of ram. – aaaaa says reinstate Monica Mar 05 '15 at 04:05
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    https://forums.freenas.org/index.php?threads/ecc-vs-non-ecc-ram-and-zfs.15449/ is probably worth a read – Håkan Lindqvist Mar 05 '15 at 07:15
  • @fukawi2 "Is there any reason ZFS or FeeeNAS *specifically* would require ECC memory, or suffer especially when running on a system using non-ECC memory?" Yeah, that's definitely a dup. Sorry I didn't see that before posting my question. I'd vote to close, but don't have the rep here for that yet. – Ajedi32 Mar 05 '15 at 14:05
  • Mouse over the down arrow; the popup says "*This question does not show any research effort; it is unclear or not useful*". Downvotes without comment may be presumed to be for at least one of those reasons. And if you want to withdraw your question in the light of the dup, the delete link is at the bottom, or you can flag it for moderator attention and ask him/her to delete it. – MadHatter Mar 05 '15 at 14:40
  • @MadHatter Right. I understand it was probably for one of those reasons. That's not very helpful though in terms of helping me improve the question, which is why I requested more specific guidance. – Ajedi32 Mar 05 '15 at 14:48
  • I'm sorry you don't like the way the voting system works on SF, but that's how it is: unlike close votes, one isn't required to give a reason when downvoting. I could speculate that it's "*lack of research*, on the basis that someone pointed out a question that had already addressed this exact issue, which can be found with a trivial site search; but that's only a guess on my part. – MadHatter Mar 05 '15 at 14:51
  • You could flag a moderator and ask for it to be closed as a duplicate, which is the correct way of handling them. – MadHatter Mar 05 '15 at 14:53
  • @MadHatter Right, I'm not saying they *have* to give an explanation, or requesting that Stack Exchange *force* downvoters to provide an explanation, (as some people on meta have). I'm just asking for an indication of what they thought was wrong to help me improve the post. "It's not useful" is okay from the perspective of giving bad questions less visibility, but not particularly helpful for me as the asker from the perspective of knowing what to improve. If they downvoted because it's a dup... well, I guess there's not a lot I can do about that. That's not a problem I can fix by editing. – Ajedi32 Mar 05 '15 at 15:00
  • @MadHatter And yes, I have flagged as a dup. (I'm pretty sure those flags don't go to mods though.) I can't close vote though, as I explained. – Ajedi32 Mar 05 '15 at 15:01
  • Fair enough; since it's now closed as a dup, all is as it should be (though I think those flags *do* go through to moderators - it's just they have lives like the rest of us, and may take a few hours to get to the flag queue). But I can't fault you in your desire for self-improvement; I may hope your next question shows more research, but I *do* look forward to reading - and trying to answer - it. – MadHatter Mar 05 '15 at 15:39
  • @MadHatter Thanks. ;-) Oh, and on the topic of dup flags, I'm pretty sure they actually go to the [close vote queue](http://serverfault.com/review/close?filter-closereason=duplicate), which any use over 3k rep should have access to. – Ajedi32 Mar 05 '15 at 15:49

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You shouldn't use non-ECC RAM on any machine that is storing or processing data you care about. This is not something that is unique to ZFS.

You're right, ZFS devs have gone to great lengths to add many layers of hashing, verification, etc. to the filesystem - all of these are of massive help in ensuring data integrity, and all of these efforts can be undermined by a single undetected single bit flip in RAM.

EEAA
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  • Yeah, I thought that might be the case. People were mentioning it so often in the context of ZFS with RAID Z that I thought perhaps it might be a specific concern with that particular RAID configuration, I guess not though. – Ajedi32 Mar 05 '15 at 02:43