Cache drive error - "Unmountable: Unsupported partition layout"

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5 hours ago, subterminal said:

I'm having issues mounting my cache drive. It keeps giving me this error:




I've tried:

  1. Stopping the array
  2. Unassigning the SSD from the array
  3. Formatting as btrfs (and even xfs once)
  4. Moving SSD back to cache
  5. Starting the arraay


I've done that several times. I've also rebooted the server a few times.


Logs attached.


Are you using UD to format the SSD?

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  • 2 months later...

Thanks for your suggestion. My MB specs say it's "PCIe Gen3 x4 M.2 Connector" (a gigabyte GA-H170M-D3H) and there's only one slot, so no chance to try anything different.  It's odd, because I can mount the device with unassigned devices, but not as a cache drive. 


One hope is that I have an external enclosure, ORICO Transparent M.2 NVME, on its way.  I'm hoping I can blow the partition mapping away there and get something Unraid compatible (GPT, 4K Aligned).  

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It still failed.  Here is the part of the log where it tries to mount the cache device.


Oct 1 12:07:50 ServerThing emhttpd: shcmd (205): mkdir -p /mnt/cache
Oct 1 12:07:50 ServerThing emhttpd: /mnt/cache mount error: Unsupported partition layout
Oct 1 12:07:50 ServerThing emhttpd: shcmd (206): umount /mnt/cache
Oct 1 12:07:50 ServerThing root: umount: /mnt/cache: not mounted.
Oct 1 12:07:50 ServerThing emhttpd: shcmd (206): exit status: 32
Oct 1 12:07:50 ServerThing emhttpd: shcmd (207): rmdir /mnt/cache
Oct 1 12:07:50 ServerThing emhttpd: shcmd (208): sync
Oct 1 12:07:50 ServerThing emhttpd: shcmd (209): mkdir /mnt/user0


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<slaps head> I finally get it...

The messaging of "unmountable -Unsupported partition layout" was tripping me up.  It made me think there was something wrong with the drive,  but that's not the problem is it. 


I put my old SSD back in and saw it too became unmountable. Then, after scrolling all the way down to the bottom of the page Main page, I see that there is an option to format an unmountable device.  <doh> All the searching and all the instruction reading did not mention this "below the fold" action that needed to be done.


All better now, thanks for helping me on this.



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I have had this problem as well and it started here and I managed to fix it temporarily it seems.

Four days ago I woke up to my server switching on and off trying to get a parity check going.


Up until now I am not sure what had happened during the parity check with the Kingston 1TB nvme but it was so severe that my system would switch off and back on even with a rescue disk.

I was convinced that the power supply was broken, even though I checked it with a PSU meter. To be safe I ordered a new one. I am hoping I can still cancel it.

After a memtest, HDD test, I noticed the problems with the reboot would start when the nvme was inserted in the system.


Somehow I managed to clone the contents of the Kingston to a different M.2 I had laying around. I formatted the Kingston and cloned the information back onto it.

After putting it back into the server I could mount it with Unassigned Devices but UNRAID would not accept it.

‘unmountable -Unsupported partition layout'


After searching the forum I stumbled onto this great post and found the format button all the way down on the MAIN page of the UNRAID GUI.

The correct way to upgrade a cache drive is to format it with the format button on the MAIN page and rsync the files back from a backup.

Cloning will just not work.


Propositions to fix some problematic things:

  1. I would urgently ask for the feature that if the system has detected 3 concessive attempts to do a parity check but could not be completed. That UNRAID starts with the array switched off and a error message of some sorts.
  2. A more user friendly way to let people know how to upgrade a cache drive?
  3. I know and understand why the format button was placed there because it can format all unmountable -Unsupported partition layouts. But for the sake of someone sanity is it possible to have the format button inside the same row for all applicable cases just like Unassigned Devices has it?





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