Changing use of SSDs from Cache to StoragePool does not work

Hi,
I have a QNAP TS453D, FW 5.2.7.3297.
HDD: 4xWD 3TB (WD30EFRX-68EUZN0**)** in Raid 5 configuration, as a Storage-pool hosting a thick volume
SSD: QNAP QM2-2S-220A hosting 2x Samsung 860 EVO 500GB

  1. Initially I set up the StoragePool with raid5 HDD array.
  2. Trying to speed communication up I added QM2+2 SSDs
    1. SSDs configured as Raid 1
    2. activated as read/write cache
    3. caching activated for the hdd StoragePool
  3. as caching does not speed up things very much in my use case I would rather use the SSDs in a Qtier configuration or as separate StoragePool with higher speed
    1. switched off and removed caching
    2. SSDs appear greyed out in the “DISKS/VJBOD” list and show as “Free” in the UsedType
      1. in this state SSDs cannot be used for new volumes/storagepools,…
      2. tried to do “secure erase” –> did not help (even after restart)
      3. tried to switch of nas, unpower nas or even disassembly QM2 to ensure empty ram-memory –> did not help
      4. final step: put SSD into a windows 11 pc and make them GPT type. Windows shows drive as Uninitialized, no partitions (at least in Windows DiskMgmt) visible
      5. back into NAS: same problem
      6. SSDs are still greyed out BUT if I experimentally open the “Create SSD Cache” dialogue, the SSDs are eligible
        1. tried to reestablish the Caching: works again

I have now run out of ideas, how to force the nas to “forget” or initialize the SSDs to start a fresh life.

Any ideas would be highly welcome.

And the exsiting storage you have is indeed a storage pool or is it a static volume ?

yes, it is a storage pool containing:
-the main thick volume with more than 90% of the space
-a thin volume with additional encryption
-two small hybrid mount volumes for cloud sync

With status “free” you should be able to assign the disks to qtier (will probably also not help you with speed btw)

I would put the system volume on it to speed up apps (default install location for apps)

No, I cannot add the SSDs to any storage type:
-creating a new Storagepool does not work (ssds are greyed out) neither with nor without QTier enabled
-adding SSDs to the existing pool doesnt work
-formatting them as “new volume”: same problem

If manual removal and clearing does not work..best to open a ticket