According to your description, it seems that the only solution you can take is to reformat your G-Raid 3 drive. Provided that you get so many files and data on your drive, you need to transfer all of them to another one first. Data transfer time depends on the size that you want to move, I recommend you clone the whole drive with iBoysoft DiskGeeker here which clones your disk in a stable and fast manner.
Step 1: Free download and install iBoysoft DiskGeeker on your Mac computer.
Step 2: Connect the G-Raid 3 disk and the target external hard drive to your Mac.
Step 3: Launch iBoysoft DiskGeeker on your Mac. Click Clone from the right toolbar.
Step 4: Determine the source device and the destination device for the disk clone work.
Step 5: Click the Start Clone button to begin the cloning process. The cloning process can't be terminated by a user. If the process is terminated by accident, the disk cloning will resume automatically after two disks are connected to Mac again.
After you move all the files to another drive, you can format your G-Raid 3 disk then. Here is how to format an external hard drive on Mac:
Step 1: Connect the external hard drive with your Mac, and the computer will mount your external hard drive.
Step 2: Launchpad → Other → Disk Utility, and click the Disk Utility.
Step 3: Choose your target external hard drive or volume, and click Erase on the top.
Step 4: Edit the disk name, and select a format and a scheme.
Step 5: Click Erase to format your target disk.
Step 6: Click Done, and congratulations that you have finished all the steps.