Hello, I wasn't sure where to ask correctly so I try here.

I noticed something weird when my scheduled parity check has been running for two days and hasn't moved past 35%. When I checked I saw that it was running at between 0.3 and 2 MB/s.

When I checked the drives one of them showed a reallocated sector count error and it has been going up since. It now says failing now in capital orange letters.

(Ignore UDMA CRC error count, that was because of bad SATA cables I have used previously. I have replaced those, I just don't know how to clear that statistic.)

I stopped the parity check and spun down all drives as I don't want to annoy the failing drive more than necessary. I am not sure what my next move should be. I do not have a replacement drive right now and I am not sure if I should back up the failing drive as it also says something about corruption errors. Don't want to overwrite good data with corrupted ones.

Should I just yank it out, make a new config and rebuild the data from parity? (I have 2 parity disks because I use recycled and usually older drives.)

I wasn't really 100% sure so I wanted to ask before I do anything dumb.

I also have a SMART test done yesterday and current diagnostics here if that helps in any way.littleboi-diagnostics-20250804-1744.ziplittleboi-smart-20250804-1741.zip

Thanks in advance

There are constant errors logged as a disk problem, and SMART looks terrible; that disk should be replaced.

Yeah, I knew that drive was on its way out because they are all used and old. I just don't have a replacement right now and when I buy one, I also have to upgrade my second parity disk (because parity needs to be the largest one I think?).

Could I pull it out and rebuild the data from parity without losing data or do I have to do something first? I would do it with the new config tool. This is the first time I have to do something like this and I don't want to lose anything.

1 hour ago, myplaybox said:

Should I just yank it out, make a new config and rebuild the data from parity?

You DO NOT do a New config when you have a drive to rebuild, the whole point of it is to make Unraid forget the current layout and start fresh, discarding the information that would be needed to rebuild.

You can just pull it out and run emulated until a new drive is available to rebuild onto.

Edited August 4, 2025Aug 4 by Kilrah

Oh I see. So is it not possible to downsize a setup in a case like this?

When I buy a replacement right now, I would buy a larger one. But that would mean I have to change the parity drive too. Isn't that a problem having two drives replaced?

Because when I buy let's say another 8 TB drive now I would have to use it as the second parity disk (because parity needs to be the largest one). Which means I would have to put the current parity 2 disk into the array. That would mean two disks have to rebuild at the same time right? Is that a problem or does that just work?

Am I thinking wrong?

I think what i would do is

• Remove Parity 2

• Start, now running array in normal state with 1 parity

• Remove failing drive, start, now array degraded with the failing drive emulated

• Assign the 3TB that was parity 2 as replacement for the failed drive, let it rebuild

• Once you have your new 8TB assign it to parity 2.

@Kilrah suggestion makes sense. You do not seem to have many drives so perhaps having 2 parity drives is overkill especially if you have a good backup strategy.

The other possibility would be to use the Parity Swap procedure to upgrade parity2 to a larger size and rebuild the failing drive onto the old parity2 drive.

20 hours ago, Kilrah said:

I think what i would do is

• Remove Parity 2

• Start, now running array in normal state with 1 parity

• Remove failing drive, start, now array degraded with the failing drive emulated

• Assign the 3TB that was parity 2 as replacement for the failed drive, let it rebuild

• Once you have your new 8TB assign it to parity 2.

Thanks, I was thinking way too complicated. Sorry for getting back to it so late, I was at work until now. I did it exactly that way and it is rebuilding now. The content all seems to be there, I was just a little scared. Rebuild will take around 5 hours now, so I will just wait and see. Thanks you are a lifesaver.

18 hours ago, itimpi said:

@Kilrah suggestion makes sense. You do not seem to have many drives so perhaps having 2 parity drives is overkill especially if you have a good backup strategy.

The other possibility would be to use the Parity Swap procedure to upgrade parity2 to a larger size and rebuild the failing drive onto the old parity2 drive.

I do not have a good backup strategy in fact. My only "backup" is this Unraid system. I am planning another server (nothing too crazy) with the sole purpose of backing up all data from my Unraid once every 2 months or something.

Is having two parity disks overkill? Since I mainly use old and recycled drives (sometimes bought second hand) I thought it would make sense to have two.

A brand new 8 TB drive is ordered and on its way now. I planned on installing it as a second parity again. Do you really think it is unnecessary?

Also thanks, I didn't know about the parity swap feature, will read into it a little more.

2 hours ago, myplaybox said:

My only "backup" is this Unraid system

You really should have backups held off the server for anything that is important to you. Parity protects you against a drive failing but does not protect you against anything going wrong at the software level that might lead to a file system being corrupted.

36 minutes ago, itimpi said:

You really should have backups held off the server for anything that is important to you. Parity protects you against a drive failing but does not protect you against anything going wrong at the software level that might lead to a file system being corrupted.

Yeah for that I am building another server as a backup. Probably running TrueNAS or something so I am not solely relying on Unraid.

Just to back up the data automatically once a month or something.