tar: write error: unexpected EOF

I am taring to disk and get this message:
tar: write error: unexpected EOF
This message is normally associated with tape devices, not disk.
Here is the syntax:
tar -cf <tarfilename> /dir
Have you seen this message on disk tars?

Is the disk/partition full, or have you exceeded your quota?

No; there is 3TB left in this partition. I am only taring 18GB.

However, for whatever reason root is 100%.

problem resolved: my target path pointed to root.