Trouble with backing up files from an external drive

So I’ve setup urbackup on my UNRAID server (installing the urbackup docker, on an old Dell Optiplex). My most crucial files I want backed up are stored on an external drive which I have always connected to my windows PC.

I’ve added the external drive (F:) to the backup paths.

I was surprised that the backup began immediately and left it on over night. When completed the “File backup status” read:

Completed with Issues

Whenever a full image backup of volume “F…” commences, it is met with:

Request of image backup failed. Reason: Creating shadow copy failed. See client log file for details.

On full file backups, I was met with the log:

backupcom->AddToSnapshotSet(&(Server->ConvertToWchar(selected_vols[i])[0]), GUID_NULL, &additional_refs[i].volid) failed. VSS error code VSS_E_VOLUME_NOT_SUPPORTED
Creating snapshot of “F” failed.

I can’t tell if the backup failed completely or if this error is only occuring on certain files. Because looking at the sum of images and files backed up. It totals to 2.02 TB (approximately the size of all the paths I selected)

Is there any issue with backing up an external drive? Attempts to find information on this topic results in posts on how to backup TO an external drive.

Any help will be greatly appreciated

Did you look at the Windows event log by chance? I have had this happen on drives and the error pointed to a disk error, which ended up being one or many bad sectors. Not saying this is the problem, but maybe just for kicks have a look. Match up the time of failure with the Windows even log and see if you get a hit.