It looks like you installed channels to run on the usb. You don’t want to do that. Save a backup of channels dvr and move the recordings you want to save, unplug the usb and leave it unplugged. Reinstall channels dvr so that it’s on the systems ssd. Install it to the home directory per above instructions link.
Mount the usb drive (right click it mount if it’s not mounted) use the search and find disks. Reformat using disks to ext4 format.
Next you want to setup the system to auto mount that drive on start up. To do this:
Use the "Disks" app.
Load the Disks app (In System) and select the disk with the filesystem you want to mount on startup.
Then select the filesystem on that disk and click on the gears (for configuration).
Select "Edit Mount Options" from the popup menu.
On the setup options, click to check the "Mount on Startup" box. (This will add the entry to fstab when you click on "OK").
Reboot, and your filesystem should be available.
Setup your storage location in channels dvr to the usb and move your recordings back on to it
