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What would be the benefit of scanner in my case

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Considering i will use snapraid and update parity drive + checksums everry night.

In what scenario would Scanner be of benefit to me if :

1/ i am also using ECC memory 

2/ without using ECC memory

 

By scenario, i mean in what practical cases it would recover from or prevent corrupted date ?

 

(i just want to measure the possible benefit before adding a layer to my NAS media center).

 

Also : when does scanner check the parity ? anytime the file is open ? and or / scheduled ? and or ?

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I don't see how ECC memory comes into play into all this. The benefit is that Scanner may be able to warn you of a drive that is starting to fail based on SMART data. Also, if sectors become bad, it would pick that up during a scan (I don't know snapraid, if it reads *every* file every night then that should be close although Scanner also checks sectors not currently in use).

Scanner checks drives depending on a schedule that you can set (and you can force scanning of individual drives at any time through the GUI).

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ECC memory is supposed to be able to autocorrect on the fly 1 bit of corrupted data in memory.

With ECC then only HDD corruption could be considered (i do not consider corruption from cpu). For only HDD data corruption, then snapraid does answer to the problem as long as it s a per request check. But snapraid doesnt do it every time the file is opened for example, only when the bacth scan will be launched (though its enough in my case).

I was more wondering if scanner would be of any benefit if not using ECC memory compared to the case where you could use ECC memory ...

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ECC memory is supposed to be able to autocorrect on the fly 1 bit of corrupted data in memory.

With ECC then only HDD corruption could be considered (i do not consider corruption from cpu). For only HDD data corruption, then snapraid does answer to the problem as long as it s a per request check. But snapraid doesnt do it every time the file is opened for example, only when the bacth scan will be launched (though its enough in my case).

I was more wondering if scanner would be of any benefit if not using ECC memory compared to the case where you could use ECC memory ...

Or another way to say it : if scanner does allow me to use non ECC memory with a result as good as if i used ECC memory without scanner, then i would be interested because chossing ECC memory does limt a lot the choice of other components … unless price doesnt matter

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I think I understand now. As you say, ECC can correct some corruption in memory, say a bit erroneously flipping. Scanner does not correct the same type of corruption on a HDD. Scanner, aside from polling SMART data, periodically checks whether it is able to read an entire disk. If a bit on a disk is simply flipped (aka bit-rot I think) then Scanner won't pick that up. Scanner will pick up unreadable sectors (and file system issues as it also does a CHKDSK AFAIK), even if they are presently not used to store data. Unreadable sectors anywhere on a drive is an issue IMHO.

But if you force snapraid to read everything periodically and have ECC memory to avoid the (remote IMHO) risk that a files' representation becomes corrupted in memory (while OK on the drive) then I guess it gets you could say it gets close enough.

 

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Having the ECC memory reduces the number of places that corruption can occur.

But the CPU (if damaged or overclocking) can still cause issues.
But there are also:

Issues with the storage controller,
Issues with the connectors,
Issues with the cables,
Issues with the power,
Issues with the drive's controller or firmware
Or even, software on the host system. 

StableBit Scanner does perform a surface scan of the disk, which is a sector by sector read of the entire disk. This can catch both issues with the disk platter, or even communication issues. 

 

Having ECC or parity protection, in general is to find random bit flips.  So it's good for detecting outright corruption of the data.  However, random bit flips are exceptionally rare (like, urban myth level of rare).  And StableBit Scanner doesn't detect this version of "bitrot". It is for detecting the sections of the disk where the bit state has gotten "fuzzy".  The read of these sections can cause the disk's firmware to fix them, or to remap them internally, before they become inaccessible.  Or to let you know when they are no longer accessible.   So it solves different problems. 

However, I'd still recommend the ECC memory, in general.  If it's not much more expensive than non-ECC, then no reason not to.

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