dump aborts; backsup device size issue?

[Warren Block]

On Mon, 2 Jun 2014, Robert Huff wrote:

> 	I have an external hard drive connected by eSATA; it looks like this:
>
> 			    used   free 
> /dev/gpt/backup    451G     10G    405G     3%    /backup
>
> 	However, when running dump this morning I got:
>
> /backup clean
> Disk mounted
> Using /backup/Mon
> Dumping to /backup/Mon/root
>  DUMP: Date of this level 0 dump: Mon Jun  2 01:59:03 2014
>  DUMP: Date of last level 0 dump: the epoch
>  DUMP: Dumping snapshot of /dev/gpt/root (/) to 2014.Jun.2.root.dump
>  DUMP: mapping (Pass I) [regular files]
>  DUMP: Cache 32 MB, blocksize = 65536
>  DUMP: mapping (Pass II) [directories]
>  DUMP: estimated 1067897 tape blocks.
>  DUMP: dumping (Pass III) [directories]
>  DUMP: dumping (Pass IV) [regular files]
>  DUMP: End of tape detected
>  DUMP: Closing 2014.Jun.2.root.dump
>  DUMP: Change Volumes: Mount volume #2
>  DUMP: fopen on /dev/tty fails: Device not configured
>  DUMP: The ENTIRE dump is aborted.
>
> 	(System =
> FreeBSD 11.0-CURRENT #1 r264673: Sat Apr 19 09:43:10 EDT 2014 amd64
> 	)
> 	So ... trying to dump < 2 gybtes onto 405 free and "end of tape"? 
> I'm confused.
> 	(I could reformat the disk, but I'd like to avoid that if possible.)

Please show the dump command options used.  In particular, do you have 
-a?