How does bitrot protection actually work?

I have read and re-read this post many times and it is full of useful info.
I am just concerned about the following quote.

Nhellie wrote:
As per release notes, "Support bitrot data protection. Automatically detect and correct corruption due to media degradation.", for me this means that as soon as you enable BitRot protection, the NAS will scan-detect-fix corruptions on the data.

To me this reads as proactively scanning the data, and I am not convinced this is how it works.
i.e. If I put data on my ReadyNAS (with snapshots) and never updated it for 5 years, would bitrot be detected?
The above suggests yes, I think it might be no, BUT I really don't know :?

RAID-10 would work.

RAID-10 certainly has redundancy. Netgear will need to confirm that their bitrot feature supports RAID-10 (seems likely though).

StephenB wrote:
BaJohn wrote: mdgm wrote: You need to be using a md raid level that provides redundancy. Does that include RAID10 as like what I have on my RN516 with 6 x 4TB. Or are you talking about RAID5 and RAID6 only. Just to clarify your question - I think you are actually wanting to know if the bitrot protection is supported for RAID-10?

By default the bitrot protection (BRP) on my RN516 is OFF.
I assumed that as the button was there, it was supported regardless of RAID although it MAY not make sense for certain RAID levels.
I was trying to clarify whether RAID-10 has redundancy in the way you mean it, and hence it is a good thing to have BRP ON.
Perhaps that is the question to be answered :)

StephenB wrote:
...I do have defrag, balance, scrubs, and disk checks scheduled in the maintenance schedule (each is run once every three months on each volume).

Could you advise the optimum order for the
1. Disk Defragmentation
2. Disk Balance (Not certain what this means - comment please?)
3. Data Scrubbing (Incorrectly described as Disk Scrubbing in the forums, which is something else entirely)
4. Disk Checks (CHKDSK ?)
if you do these end to end (or a day apart, say).
OR
do you spread them randomly/evenly through your 3 month period?

BaJohn wrote:
mdgm wrote: You need to be using a md raid level that provides redundancy. Does that include RAID10 as like what I have on my RN516 with 6 x 4TB. Or are you talking about RAID5 and RAID6 only.

Just to clarify your question - I think you are actually wanting to know if the bitrot protection is supported for RAID-10?

mdgm wrote:
You need to be using a md raid level that provides redundancy.

Does that include RAID10 as like what I have on my RN516 with 6 x 4TB.
Or are you talking about RAID5 and RAID6 only.

Fragmentation doesn't happen more on slower platforms, but defrag time of course is longer. I think all OS6 users need to be thoughtful about CoW. If there's a way to report share-by-share fragmentation (and maybe even have a fragmentation alert) in OS6, that would be a good thing.

Generally speaking, on the lower end NAS you do need to trade off performance against features. That's the "cost" of getting the less expensive platform.

But there are lots of scenarios where this is acceptable for home users. If you are using WiFi, powerline, or fast ethernet then you are usually network bound anyway, so the performance hit isn't something you'll experience. And speed isn't the only consideration. Based on posts here, I'd personally avoid RAID-6 and SCSI LUNs on the RN100 series. But I see no reason to avoid the other features, as long as people understand that performance will drop if you turn on too much stuff.

Netgear already recommends RN300 or better for business users, which makes perfect sense to me. Some business can probably get by with less, but slower performance does translate into $$$ for most businesses.

Seeing repair is not all that constant I would think it would be the CoW fragmentation as you mentioned.

mdgm wrote:
Bitrot protection is suitable for some use cases and can be quite resource intensive. So only using it on shares for which it is appropriate to use it with is good.

Overall, I think its frustrating for RN100 series users to be told repeatedly "hey, all these features in the GUI - they aren't for you...". Netgear should provide some real data on the performance impacts of checksums, AntiVirus, RAID-6 on all platforms. Then users can figure out if the benefits outweigh the costs for them, and make better choices on their platform investments,

Do you mean the repair is resource intensive, or the the protection itself (checksums + CoW)?

I'm not seeing much impact on my RN102, which leads me to think that the issue you are talking about is CoW fragmentation. That of course is not easily quantified - and fragmentation kills performance on all platforms.