I've replaced a crashed disk by a new one with same capacity.

Made a 'New Config', started the array and rebooted.

In 'Main' view, everything looks correct.

But I was wondering why there's never any activity on that disk.

Looks like the disk is not mounted correctly.

Edit: S.M.A.R.T runs with no problems and does not show any errors.

What can I do?

Edited December 20, 2025Dec 20 by Codierknecht

Disk Log Information

Please post the diagnostics.

Here's the diag.

I'm currently trying to remove the drive from btrfs and then add it again.

diskstation-diagnostics-20251221-1012.zip

7 minutes ago, Codierknecht said:

I'm currently trying to remove the drive from btrfs and then add it again.

Don't do that, please wait a few minutes so that I can check the diags.

Try this:

Stop the array and reimport the pool with the 3 good devices:

on main click on the first device for that pool and then "remove pool"

back on main, create a new pool with the same name and 3 slots

assign the first 3 pool devices (sdb, sdc and sdb), leave the filesystem set to auto

start the array to import the pool degraded, raid4 should show a red x

Then stop the array, assign the other device to that slot, and start the array.

Any issues post new diags.

Done exactly as recommended ... same result ☹️

diskstation-diagnostics-20251221-1110.zip

I can add the drive to btrfs with no problem.

52 minutes ago, Codierknecht said:

Done exactly as recommended ... same result

Device 4 is not being used to replace the missing device; it may need to be wiped first.

49 minutes ago, Codierknecht said:

I can add the drive to btrfs with no problem.

But since you now added to the pool, you will need to manually remove the missing device, then reimport the pool with the 4 existing devices.

With the array running type

btrfs dev remove missing /mnt/raid

once that's done, reimport the pool as before, but with the 4 devices

23 minutes ago, JorgeB said:

once that's done, reimport the pool as before, but with the 4 devices

Currently removing the missing drive.

This will take an amount of hours ...

That should be instantaneous unless it's doing a rebalance for the new added disk.

Hmmmm, now it's no longer mountable ☹️

diskstation-diagnostics-20251222-1113.zip

I was able to mount it 'degraded'. After a reboot the pool is up and running again.

My inner Monk would prefer ID's without gaps. But that's some kind of luxury problem ;-)

Thanks so far and have a happy christmas time.

Dec 22 11:12:24 DiskStation kernel: BTRFS warning (device sdb1): cannot mount because device replace operation is ongoing and

Dec 22 11:12:24 DiskStation kernel: BTRFS warning (device sdb1): srcdev (devid 4) is missing, need to run 'btrfs dev scan'?

Dec 22 11:12:24 DiskStation kernel: BTRFS warning (device sdb1): cannot mount because device replace operation is ongoing and

Dec 22 11:12:24 DiskStation kernel: BTRFS warning (device sdb1): tgtdev (devid 0) is missing, need to run 'btrfs dev scan'?

It looks like the edvie replace was still ongoing, with the pool mounted degraded post the output of btrfs fi usage -T /mnt/raid

I've canceled the ongoing operations.

root@DiskStation:~# btrfs fi usage -T /mnt/raid

Overall:

Device size: 14.55TiB

Device allocated: 2.75TiB

Device unallocated: 11.81TiB

Device missing: 0.00B

Device slack: 14.00KiB

Used: 2.73TiB

Free (estimated): 5.91TiB (min: 5.91TiB)

Free (statfs, df): 5.74TiB

Data ratio: 2.00

Metadata ratio: 2.00

Global reserve: 512.00MiB (used: 0.00B)

Multiple profiles: no

Data Metadata System

Id Path RAID10 RAID10 RAID10 Unallocated Total Slack

-- --------- --------- -------- --------- ----------- -------- --------

1 /dev/sdb1 789.00GiB - 16.00MiB 2.87TiB 3.64TiB 3.50KiB

2 /dev/sdc1 788.00GiB 2.00GiB 16.00MiB 2.87TiB 3.64TiB 3.50KiB

3 /dev/sdd1 788.00GiB 2.00GiB 16.00MiB 2.87TiB 3.64TiB 3.50KiB

5 /dev/sde1 445.00GiB - 16.00MiB 3.20TiB 3.64TiB 3.50KiB

-- --------- --------- -------- --------- ----------- -------- --------

Total 1.37TiB 2.00GiB 32.00MiB 11.81TiB 14.55TiB 14.00KiB

Used 1.36TiB 1.65GiB 192.00KiB

The pool is currently not degraded, though it looks like it's not totally balanced.

Already started balancing ...

Perfectly balanced now :-D