Getting Errors on (2) relatively new drives during parity check. Logs attached if someone can suggest how to proceed.

Hoping I can just stop the check and re-seat the cables to those drives and start check again. Not sure how to evaluate that from the logs.

media-server-syslog-20260201-1231.zip

The file you posted is empty!

With errors trying to build parity it will be invalid anyway so no point in continuing. Do what you suggest, and if that does not work post the diagnostics.zip file for your system to your next post in this thread.

2 hours ago, itimpi said:

The file you posted is empty!

With errors trying to build parity it will be invalid anyway so no point in continuing. Do what you suggest, and if that does not work post the diagnostics.zip file for your system to your next post in this thread.

Huh, wonder why it was empty?? Ok, stopping now and will check cabling ASAP. Thank you!

EDIT: I am including the diagnostics here now in case you are able to look and suggest the culprit or if I have a bigger issue. Thx

media-server-diagnostics-20260201-1538.zip

Edited February 1Feb 1 by wdpaynter

Disk15 is disabled now. When it couldn't be read Unraid tried to write its calculated data back to it and when that failed it was disabled.

Same thing happening with disk16, but since you have single parity and disk15 was already disabled, it couldn't be disabled.

So, instead of checking parity, now you need to rebuild disk15.

SMART for both disks looks OK and emulated disk15 is mounted.

Looks like these disks are on different controllers.

How are these disks powered? Ideally, no more than 4 drives per PSU cables. MOLEX - SATA splitters are better than SATA-SATA splitters.

I recommend dual parity with so many disks.

15 hours ago, trurl said:

Disk15 is disabled now. When it couldn't be read Unraid tried to write its calculated data back to it and when that failed it was disabled.

Same thing happening with disk16, but since you have single parity and disk15 was already disabled, it couldn't be disabled.

So, instead of checking parity, now you need to rebuild disk15.

SMART for both disks looks OK and emulated disk15 is mounted.

Looks like these disks are on different controllers.

How are these disks powered? Ideally, no more than 4 drives per PSU cables. MOLEX - SATA splitters are better than SATA-SATA splitters.

I recommend dual parity with so many disks.

OK thanks!

I just powered down and I am going to look at cables. I have had power/cable issues in the past. I have since changed my splitters to MOLEX-SATA instead of SATA-SATA and made sure not to have too many per PSU connection per the recommendation here on this forum. I haven't had a problems in many months. I have 18 drives in my server and have no room for more, so I bought a new 18TB HDD to try to consolidate (2) 8TB drives onto it and then planned to add a second 18TB Parity drive, just haven't been able to do step one first to make room

EDIT: an update regarding wiring. I have most of my drives being powered by MOLEX to SATA splitters (1x4). I have (2) SATA leads coming from PSU. One had (2) drives connected directly (no splitter) and (2) connected via a 2x1 SATA splitter. The other had (2) drives connected via a 2x1 SATA splitter and the case power and/or fan connected directly. I moved (1) drive from the first to the second via a direct SATA connection. So now I have (3) drives on each (though one also has the case power). Though each lead does have a 2x1 SATA splitter which is unavoidable with my setup. Do you think this may help a little?

EDIT2: I am attempting to rebuild disk15 onto itself. Thx

Edited February 2Feb 2 by wdpaynter

2 hours ago, wdpaynter said:

Do you think this may help a little?

yes

Also make sure all cables have enough slack so they aren't pulling on the connections. And don't bundle data cables (crosstalk).

50 minutes ago, trurl said:

yes

Also make sure all cables have enough slack so they aren't pulling on the connections. And don't bundle data cables (crosstalk).

Got it. Thanks!

So once disk15 rebuilds, start a parity check again? What about disk16? both of those discs were on the same PSU lead, but are no longer (as described above)...

Edited February 2Feb 2 by wdpaynter

During rebuild, you should see lots of writes to the rebuilding disk, lots of reads from all other array disks, and zeros in the errors column for all disks.

If rebuild completes without errors, I see no need for a parity check but of course you can do and it should also complete with no I/O errors or sync errors.

3 hours ago, trurl said:

During rebuild, you should see lots of writes to the rebuilding disk, lots of reads from all other array disks, and zeros in the errors column for all disks.

If rebuild completes without errors, I see no need for a parity check but of course you can do and it should also complete with no I/O errors or sync errors.

Ok, and you think if the rebuild results in zero errors on disk 15 that it likely means that disk16 is also fine and it was just cabling/power issue? Thx!

4 minutes ago, wdpaynter said:

rebuild results in zero errors on disk 15 that it likely means that disk16 is also fine and it was just cabling/power issue?

4 hours ago, trurl said:

zeros in the errors column for all disks

Post new diagnostics after rebuild completes, or if any disk begins to show errors in the errors column.

Oh, shoot. I see now. I guess ALL the discs are read in order to write to the rebuild. Sorry. I am (slowly) starting to better understand how this works. Thx

16 minutes ago, wdpaynter said:

I guess ALL the discs are read in order to write to the rebuild.

Here is a deeper dive I did recently on this:

On 1/28/2026 at 11:26 PM, trurl said:

parity doesn't contain any of your data and it couldn't possibly have the capacity by itself to recreate any and all of your other disks. It might be able to be a backup of a single disk, but that isn't what it is. It needs to be able to help rebuild any disk, not a particular single disk. Parity plus all other disks allow the parity calculation to provide the data for a missing disk.

On 1/28/2026 at 11:45 PM, trurl said:

When a disk is disabled, it isn't used again by Unraid until it is rebuilt, or New Config accepts it back into the array. Instead, the disabled disk is emulated by reading parity and all other disks and calculating the data for the disabled disk. Even if the original disk is destroyed, the emulated disk can be read in this way. And the emulated disk can be written by updating parity as if the disk had been written, so those writes can be recovered by rebuilding. The initial failed write that caused the disk to be disabled is emulated, and all writes to that disk after that

On 1/28/2026 at 11:45 PM, trurl said:

Parity is very simple. If you're interested, follow this link

https://docs.unraid.net/unraid-os/getting-started/what-is-unraid/

then expand the Software Defined NAS section and then expand the How Parity Works section under that.

Thanks! I appreciate some insight. So would it have been better to do the new config so that repeated failed writes are not included on parity? Or is that insignificant?

Edited February 2Feb 2 by wdpaynter

The whole point of parity is to allow things to keep working until you can rebuild the disk. If you New Config any time you have a disk problem, there is no point in having parity.