I had 2x6TB drive and a JBOD volume because the data isn't really critical and couldn't afford to lose half the space for a raid 1.
Now (a couple years later) I bought 2x8TB new drives for my 4 -bay synology.
This is where I made the mistake of adding the drive to my JBOD storage Pool. I have 4 HDD now so I need to switch to a real raid to support drive failure. With 4 drives on a JBOD I increase the risk of data loss a ton!
I haven't increased the logical volume and filesystem containing my data but the disks are part of the JBOD storage pool and synology doesn't allow to remove them from the WebUI.
I spent some time trying to remove the drives from the raid with the shell but wasn't successful.
Using "pvresize --setphysicalvolumesize 11436928 /dev/md2" I was able to shrink the physical volume to what I think used to be its size.
Also with mdadm I marked the new drive as failed and reassembled the linear raid without them but then "vgs" throw out read errors and i'm unable to mount my data.
It seems that some part of the raid setup still require the new disks and I'm not removing them properly.
Good thing is i'm able to cancel everything I did in the shell and mount my data which is still there and taking less than half my total HDD space but i don't know how to proceed.
How can I remove those new drives from the JBOD and use them to migrate to SHR or RAID5/RAID6 without losing my data ?
Edit : Screenshots to help better understand the situation : https://imgur.com/a/LpGCjC2 The new drives are actually 1 and 2