What does it mean when I get hashcheck failures? I presume this means something about the parity data being not correctly updated. But what is the difference between a failed hashcheck and a need to update?
I've been experimenting with disParity for the past few days. Nearly every time I do a hashcheck I get failures. Right after updating parity, right after restoring a drive, after undeleting. Whats up with that?
Hashcheck failures aren't normal. It means the contents of a file appears to be different from when disParity added it to the backup. In theory the purpose of the command is to detect file corruption caused by a failing hard drive.
If you are getting a lot of hashcheck failures, there are 3 different possibilities that I can think of:
1. Some other app is modifying files on your drive after you last ran an update.
2. One of your hard drives is failing.
3. There is a bug in disParity.
I'm guessing #1 is probably the most likely cause.
Is there any pattern to the files that are failing the hashcheck? Are they all of the same type? All on the same drive? Have they all been recently modified?
I wouldn't be surprised if it was #2. I am testing disParity out on three old hard drives hooked up with USB.
I will format them, put different data on them and see if I can follow a pattern.
"It means the contents of a file appears to be different from when disParity added it to the backup."
How is this different from scanning and seeing if the disk is up to date? I assume that is done via hashcheck... ??
Thanks for your time!
How is this different from scanning and seeing if the disk is up to date? I assume that is done via hashcheck... ?
Well, the "scan" process does a lot more than just hash checks. It builds an inventory of every file on the drive and compares it to the last known list, checking for new files, deleted files, moved files, and edited files. Hash checks are only used during a scan to check if a) a file that appears to have been moved is in fact still the same file (in which case the parity data doesn't need to be updated), and b) a file that may have been edited (based on its Last Modified timestamp) has in fact changed.
Meanwhile, the "hashcheck" command re-calculates the hash value of every file on the drive, which is a far more intensive and time consuming process than a scan.
so a "hashcheck" is primarily used for data consistency/rot check?
The "Hashcheck All" button in the UI, yes.
I have some hashcheck failures. When a hashcheck fails, can disparity rebuild the file from the array, and hopefully fix it?
Yes. You'll have to delete the file first so that you can "undelete" it from within disParity, which will restore it from the array. (In case anything goes wrong, don't actually delete the original file, just move it to another drive.)
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