It occurred to me yesterday, while trying to restore a file that had somehow been corrupted, that it would be nice to be able to read from an emulated drive and try to recover the file without having to remove the drive from the array temporarily. In my case, I was able to get the file from the emulated drive, after removing the drive that contained the corrupted file, and it was indeed a proper file.

 

Seems like this could be a quick first step for restoring a corrupted file locally before having to resort to pulling a remote backup. If mounting is not feasible, due to file system locks or something similar, perhaps a command could be included in unraid to be able to rebuild a particular file on a specific disk from the parity and the other disks. Something like below would be great.

 

parity-restore /mnt/disk2/somefile.txt /mnt/user/somefile.txt.restored

 

In practice this command would rebuid /mnt/disk2/somefile.txt from the parity disk as well as the other disks, save disk2 of course, and save it to /mnt/user/somefile.txt.restored.

 

Any chance for this, unless there is already a way to do it.

Edited May 14, 20242 yr by EldonMcGuinness

I doubt that parity could recover corrupted file.

 

If recover become true , it just because some how integrity issue and lucky recover the file.

Well parity should be able to, and at least did for me, just fine. Consider this situation:

• You have 6 disks
• Disk 1 through 6 being found at /mnt/disk1 through /mnt/disk6.
• Parity checks are not set to correct the parity drive, meaning if a discrepancy is found one could still read the previous parity (checked?) version.

This means is say /mnt/disk2/somefile.txt were to suffer from bitrot, overwriting, or really anything else (EDIT: Forgot parity is actively written, thanks @primeval_god) one can pull disk2 from the array and then access the parity (checked? is this the right term) version.

 

Seems like a logical conclusion to me. Kinda like having a non-versioned backup. Assuming you have not overwritten the backup with bad data you could restore from it.

Edited May 14, 20242 yr by EldonMcGuinness

Its a cool idea, but unlikely to be helpful except for the rare case of actual bitrot. For things like overwrite, accidental deletion, corruption due to software error, etc. the parity drive will be of little to no help because unRAID maintains real-time parity. Any changes made to the file under normal operation are immediately reflected in parity. 

9 minutes ago, primeval_god said:

Its a cool idea, but unlikely to be helpful except for the rare case of actual bitrot. For things like overwrite, accidental deletion, corruption due to software error, etc. the parity drive will be of little to no help because unRAID maintains real-time parity. Any changes made to the file under normal operation are immediately reflected in parity. 

Ahh true, still a valid solution for bitrot or other possible corruption issues of that nature that are more of a passive issue.