Done, works, but the process was a little bit more complicate.
I’m describing so that it might be of help for someone else
I’m working on High Sierra, and the raid drive is g-tech thunderbolt 2 (only T plugs and usb on the back)
g-raid config does not see the hd in the format out of the box
When new/empty I reformatted to the new file system APFS, now the G-RAID CONFIGURATOR utility sees it (after a little while)
4 then I selected raid 1, executed the utility, and
after that in MAC OS Disk utility I reformatted it as asked (for some strange reason I guess one of the partitions is still in Mac Os journaled) and the disk appears as raid with 6Tera. I hope it works as Raid1 now
the process failed a few times (the Configurator gave an error message after starting the RAID1 conversion process, so I reformatted back in MAC OS journaled, and then back to APFS and started the process again)
To reconfigure your G-RAID from RAID 0 to RAID 1 with a 6 terabyte capacity, you will need to follow these steps:
Connect your G-RAID to your Mac.
Launch Disk Utility. You can do this by going to Finder > Applications > Utilities > Disk Utility.
In Disk Utility, select the G-RAID from the list of available disks on the left-hand side of the window.
Click on the “Erase” button at the top of the Disk Utility window.
In the “Format” drop-down menu, select “Mac OS Extended (Journaled, Encrypted)”.
In the “Name” field, enter a name for your new RAID volume.
In the “Scheme” drop-down menu, select “RAID”.
In the “RAID Type” drop-down menu, select “RAID 1 (Mirrored)”.
In the “Chunk Size” drop-down menu, select “256k”.
In the “Available Disks” section, select the two disks that you want to use for the RAID 1 volume.
Click on the “Create” button to create the new RAID 1 volume.
Note that creating a RAID volume will erase all data on the disks that you select. Therefore, make sure that you have backed up any important data before proceeding with these steps.