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, 20214 yr by moguiyu

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?

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.

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.

 

 

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

This is a new one, don't see how parity was corrected during a disk rebuild with single parity.

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?

 

 

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.

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.

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.

@moguiyu

Without rebooting, do a non-correcting parity check and post new diagnostics when done.

 

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

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.

 

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.