moguiyu Posted December 8, 2021 Share Posted December 8, 2021 (edited) Hi Experts here: I'm using unraid for more than a year but still new to it. today I had to change my 1TB data disk to a 4TB one by swapping it.(no additional ports to add). the steps I took was turn off the server, replace the disk; turn on the server and format the new disk, then mount Assign the new disk to replace the old and start the parity rebuild process. after around 9 hours parity recovery data rebuild, the array is working with error saying 4 errors. should I worry about it? what should I do to check? cause I still have another 1TB data disk need to change to 4TB one thank you very much in advance for your kind answer. Edited December 11, 2021 by moguiyu Quote Link to comment
trurl Posted December 8, 2021 Share Posted December 8, 2021 attach diagnostics to your NEXT post in this thread. 5 minutes ago, moguiyu said: replace the disk; turn on the server and format the new disk, then mount the new disk and start the parity process. Not sure what you mean by "mount" here. Unraid mounts data disks when you start the array, nothing for you to do yourself to "mount" it. And parity disks are not mounted because they have no filesystem. Probably you meant "assigned"? Format is NEVER part of rebuild. Was this a data disk? Quote Link to comment
moguiyu Posted December 9, 2021 Author Share Posted December 9, 2021 8 hours ago, trurl said: attach diagnostics to your NEXT post in this thread. Not sure what you mean by "mount" here. Unraid mounts data disks when you start the array, nothing for you to do yourself to "mount" it. And parity disks are not mounted because they have no filesystem. Probably you meant "assigned"? Format is NEVER part of rebuild. Was this a data disk? yes, you are right, I meant 'assign'. it was a new disk, so it need to be formatted before I can use it for anything. yes, the disk I changed was data disk, not a parity disk. Quote Link to comment
trurl Posted December 9, 2021 Share Posted December 9, 2021 5 hours ago, moguiyu said: it was a new disk, so it need to be formatted before I can use it for anything. No it didn't and the fact that you thought so is concerning. Many people have made the mistake of formatting a disk in the array thinking they can rebuild it from parity. Many people have a vague idea of what format does. They just think it gets a disk ready to use, whatever that might mean. But computers don't work on vague ideas. Format means "write an empty filesystem to this disk". That is what it has always meant in every operating system you have ever used. When you format a disk in the array, Unraid treats this write operation exactly as it does any other, by updating parity. So, after formatting a disk in the array, the only thing you can rebuild from parity is that empty filesystem you wrote by formatting. But, it sounds like you may have formatted the disk before assigning it to the array. If so, it was only pointless, not disastrous. Pointless because rebuild completely overwrites every bit of the disk regardless of what is on it, so it doesn't matter at all if you have written an empty filesystem or anything or nothing to it. 14 hours ago, trurl said: attach diagnostics to your NEXT post in this thread. Quote Link to comment
moguiyu Posted December 9, 2021 Author Share Posted December 9, 2021 2 hours ago, trurl said: No it didn't and the fact that you thought so is concerning. Many people have made the mistake of formatting a disk in the array thinking they can rebuild it from parity. Many people have a vague idea of what format does. They just think it gets a disk ready to use, whatever that might mean. But computers don't work on vague ideas. Format means "write an empty filesystem to this disk". That is what it has always meant in every operating system you have ever used. When you format a disk in the array, Unraid treats this write operation exactly as it does any other, by updating parity. So, after formatting a disk in the array, the only thing you can rebuild from parity is that empty filesystem you wrote by formatting. But, it sounds like you may have formatted the disk before assigning it to the array. If so, it was only pointless, not disastrous. Pointless because rebuild completely overwrites every bit of the disk regardless of what is on it, so it doesn't matter at all if you have written an empty filesystem or anything or nothing to it. thank you for the explanation. yes, I only format before I assign the disk of course. my question is still do I need to worry about the 4 errors? anyway to check what exactly the error is about? I'm attaching diagnostic file. m17-diagnostics-20211209-0849.zip Quote Link to comment
JorgeB Posted December 9, 2021 Share Posted December 9, 2021 This is a new one, don't see how parity was corrected during a disk rebuild with single parity. Quote Link to comment
trurl Posted December 9, 2021 Share Posted December 9, 2021 Looks like disk2 is mounted after rebuild, but Dec 8 13:54:40 M17 kernel: md: recovery thread: recon D2 ... Dec 8 13:54:40 M17 kernel: md: recovery thread: P corrected, sector=128 Dec 8 13:54:40 M17 kernel: md: recovery thread: P corrected, sector=136 Dec 8 13:54:40 M17 kernel: md: recovery thread: P corrected, sector=144 Dec 8 13:54:40 M17 kernel: md: recovery thread: P corrected, sector=152 since you only have single parity I don't see how it can correct P while rebuilding disk2. 3 minutes ago, JorgeB said: This is a new one, don't see how parity was correct during a disk rebuild with single parity. Maybe it had to go back to parity sectors it had already passed on the rebuild due to new writes? Quote Link to comment
JorgeB Posted December 9, 2021 Share Posted December 9, 2021 13 minutes ago, trurl said: Maybe it had to go back to parity sectors it had already passed on the rebuild due to new writes? I believe it's not how it works, disk is rebuilt sequentially, any writes to an already rebuilt zone should only update parity as normal, nothing would be logged. Quote Link to comment
trurl Posted December 9, 2021 Share Posted December 9, 2021 19 minutes ago, JorgeB said: I believe it's not how it works, disk is rebuilt sequentially, any writes to an already rebuilt zone should only update parity as normal, nothing would be logged. That's what I assumed but don't have any other ideas for how it could decide to correct parity when there aren't enough valid disks to allow that. Quote Link to comment
JorgeB Posted December 9, 2021 Share Posted December 9, 2021 30 minutes ago, trurl said: don't have any other ideas for how it could decide to correct parity when there aren't enough valid disks to allow that. Same, never seen that before. Quote Link to comment
trurl Posted December 9, 2021 Share Posted December 9, 2021 @moguiyu Without rebooting, do a non-correcting parity check and post new diagnostics when done. Quote Link to comment
moguiyu Posted December 10, 2021 Author Share Posted December 10, 2021 On 12/9/2021 at 6:32 PM, trurl said: @moguiyu Without rebooting, do a non-correcting parity check and post new diagnostics when done. thanks, this is without rebooting. new diagnostics of non-correcting parity check. m17-diagnostics-20211210-0900.zip Quote Link to comment
moguiyu Posted December 10, 2021 Author Share Posted December 10, 2021 Thank you all you guys for the comments, I think I have not explain it well. I was following this instruction: upgrading the 1TB data drive to 4TB data drive. the parity disk was not changed at all. I was using the rebuild process to fill the new disk with data, just the parity check shows 4 errors, I'm not sure if I should be very worried about the error. the 2nd time when I did the parity check, it show 0 errors now. Quote Link to comment
trurl Posted December 10, 2021 Share Posted December 10, 2021 1 hour ago, moguiyu said: I think I have not explain it well You explained it well enough, and our comments were completely based on your diagnostics. On 12/9/2021 at 11:22 AM, trurl said: since you only have single parity I don't see how it can correct P while rebuilding disk2 1 hour ago, moguiyu said: using the rebuild process to fill the new disk with data, just the parity check shows 4 errors It wasn't a parity check though. It was the rebuild itself that corrected parity, which shouldn't be possible with single parity since there are not enough valid disks to calculate a result for the parity disk. I'm going to see if @limetech can teach us something about this. Quote Link to comment
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