This error code seems that there is something wrong with your external hard drive like the corrupted file system or bad sectors…The urgent thing to do is recover and backup all your data with professional software if you have important files in it. iBoysoft Data Recovery for Mac, is an effective tool you can try.
- Recover data from the drive with iBoysoft Data Recovery for Mac. After free downloading, open it then click your external hard drive in the left menu, and choose Search for Lost Data at the bottom. Then preview the scanning results and choose your wanted files. Click Recover to save them to another place.
- Run First Aid a few more times.
- Reformat the external hard drive. Open Disk Utility, select the external hard drive in the left then click on the Erase. Enter the name, select the file system type, and click Erase.
If these don't work, copy your recovered data to another new external hard drive and drop this one.
Also read: Fix File System Check Exit Code Is 8 on Mac