I have 2 cache disks and all of a sudden the second one went down, I only noticed after all my docker services were offline. First thing I did was a reboot. After the reboot, the server gave me the message: "Warning [SRV-UNRAID-PROD] - Cache pool BTRFS missing device(s)". When checking the Main page, the second cache just has a red x mark, and shows device missing. The array also went offline and showed an unclean shutdown. I collected the diagnostics, see attached. I also tried a full shutdown after, left it offline for 5min and started it back up, no change.

Since I do have 2 cache disks I started the array back up with the "write corrections to parity" enabled, and now my docker services are back up and working.

Never encountered an issue like this before, so any help on what the next steps are would be highly appreciated. Thanks in advance.

srv-unraid-prod-diagnostics-20250918-2223.zip

Ched/replace cables for the missing device to see if it comes back online, also check to see if it's detected in the BIOS.

2 hours ago, JorgeB said:

Ched/replace cables for the missing device to see if it comes back online, also check to see if it's detected in the BIOS.

The cache disks are m.2 drives, so there's no cables to replace. The server is currently doing a parity check, so I don't want to shut it down to check the BIOS right now. It's done in about 7 hours, so will update the thread when it's done. Thank you.

If they are NVMe devices, do a power cycle once the parity check finishes; to see if it comes back online, just rebooting is typically not enough with those.

46 minutes ago, JorgeB said:

If they are NVMe devices, do a power cycle once the parity check finishes; to see if it comes back online, just rebooting is typically not enough with those.

Yes they are NVMe devices. I did try a power cycle after collecting the diagnostics, no change.

Try swapping slots between them and see where the problem follows.

48 minutes ago, JorgeB said:

Try swapping slots between them and see where the problem follows.

Good call. Will try that after the parity check has completed. Appreciate the help so far.

Did get a new warning from the server as well: "Warning [SRV-UNRAID-PROD] - pool BTRFS too many profiles (You can ignore this warning when a pool balance operation is in progress)"

Guessing it's just in reference to the fact that it's set up with 2 slots, but only 1 disk is attached?

This is normal in this case, since the pool is missing a device; new writes will be in the single profile, not RAID1.

21 hours ago, JorgeB said:

This is normal in this case, since the pool is missing a device; new writes will be in the single profile, not RAID1.

I tried moving one of the NVMe disks to a different slot, and after a reboot it showed 2 drives in the BIOS. I then tried moving the drive back to the original slot, and it still showed up after a reboot. So now both drives seems to be back on showing up in unraid, but unraid now tells me that there are no pools available.

How do I get the pool back online? Yesterday I had everything working with only one of the cache drives, but now one shows unmountable, and the other shows up under the unassigned devices. Is my data lost?

Post the output from btrfs fi show

1 minute ago, JorgeB said:

Post the output from btrfs fi show

Label: none  uuid: 33d7bd6e-5c15-43f5-af67-4940080c6fe4
        Total devices 1 FS bytes used 416.00KiB
        devid    1 size 1.00GiB used 126.38MiB path /dev/loop2

Label: none  uuid: a7f0f2e8-593b-403a-adfc-56feadb94442
        Total devices 2 FS bytes used 478.26GiB
        devid    1 size 931.51GiB used 577.01GiB path /dev/nvme0n1p1
        devid    2 size 931.51GiB used 567.01GiB path /dev/nvme1n1p1

Edited September 20, 2025Sep 20 by Cernel

Try reimporting the pool with both 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 2 slots

assign both pool devices (order doesn't matter), leave the filesystem set to auto

start the array to import the pool and post new diags.

6 minutes ago, JorgeB said:

Try reimporting the pool with both 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 2 slots

assign both pool devices, leave the filesystem set to auto

start the array to import the pool and post new diags.

So far so good :)

They both seem to have been added successfully. Here's the new diags:

srv-unraid-prod-diagnostics-20250920-1357.zip

The docker services won't start, and my logs are being spammed with "Sep 20 13:36:27 srv-unraid-prod shfs: assign_disk: /appdata (123) No medium found"

@JorgeB I did a reboot and got a bunch of new error messages, new up-to-date diagnostics:

srv-unraid-prod-diagnostics-20250920-1500.zip

Edited September 20, 2025Sep 20 by Cernel

Click the first pool device and scrub the pool. If all errors are corrected, after doing that, recreate the Docker image:

https://docs.unraid.net/unraid-os/troubleshooting/common-issues/docker-troubleshooting/#re-creating-the-docker-image-file

Then:

https://docs.unraid.net/unraid-os/troubleshooting/common-issues/docker-troubleshooting/#reinstalling-docker-applications

Also see below if you have any custom docker networks:

https://docs.unraid.net/unraid-os/troubleshooting/common-issues/docker-troubleshooting/#restoring-docker-custom-networks

16 minutes ago, JorgeB said:

Click the first pool device and scrub the pool. If all errors are corrected, after doing that, recreate the Docker image:

https://docs.unraid.net/unraid-os/troubleshooting/common-issues/docker-troubleshooting/#re-creating-the-docker-image-file

Then:

https://docs.unraid.net/unraid-os/troubleshooting/common-issues/docker-troubleshooting/#reinstalling-docker-applications

Also see below if you have any custom docker networks:

https://docs.unraid.net/unraid-os/troubleshooting/common-issues/docker-troubleshooting/#restoring-docker-custom-networks

Seems like everything is working. Currently reinstalling all the apps. Thanks so much for all the help.

My VMs also got deleted for some reason, but I have backups, so it should be fine.

From the scrub, there's seems to really have been some issues :)

Definitely sending you some beer money 🍻 Thanks again

Glad to hear, recommend resetting the pool stats and then monitoring for any future issues with the script from here: https://forums.unraid.net/topic/46802-faq-for-unraid-v6/page/2/#findComment-700582

Thanks for the beer money!