OS6 on a legacy device in 2018.

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TeknoJnky wrote:

 

- no you cannot go from raid 6 to raid 5. You don't necessarily have to factory default, but you would need to delete the data volume and recreate a new raid 5 volume, so the result is the same... you would have to completely backup then restore all data.

 

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Actually if you have an empty slot in the NAS, you can switch to raid-6 without data loss.  This would also require that the three largest disks currently in the NAS be the same size.

PerfectOnline wrote:

Are there any ways to verify a directory and save the results in a file so that one can do a quick check if needed? I’m not that educated in this regard but i know of some solution generating .md5 files, i just don’t know enough to put it in practise (best program and stuff like that).

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Some years ago I started doing this for selected folders (before I owned a NAS).  I still use QuickSFV (though it is old, it still works), creating an "sfv" file in each folder.  

You can also use something like QuickPar (also old) or MultiPar for this.  (I've used QuickPar, but not MultiPar).  These create signature files similar to QuickSFV, but also can create repair files from limited amounts of file corruption.  For instance, if the repair files are 10% of the folder size, they can recover from up to 10% of corrupted data blocks in the files.  This operates similarly to RAID redundancy btw, but is more sophisticated.

As you say, you can also zip (or rar) the folders - compressed archives also have built-in integrity checks.  WinRar does include "recovery records" which are similar to the par2 repair files created by QuickPar.  Of course you can't access the data as easily if you do that. 

These approaches aren't automated (and if they were, you'd risk updating the signatures when the files became corrupted). So they do take some discipline to use. I don't think it'd be practical to use them on frequently updated folders.  

FWIW, btrfs checksums will also detect corrupted files.  But it's not easy to access those corrupted files - making repair (or partial recovery) difficult.  The bitrot protection is an interesting ReadyNAS feature (which uses the checksums and the RAID partity blocks), but I haven't seen posts here from people saying that it recovered their files.  I do have it enabled, but my main strategy for protection from data loss is backups (using snapshots to protect against accidental deletion or modification).