I put two more ISO images in my backup folder. I am now backing up 5.4783 GB.  
My previous math of the 5.5 GB a minute using tar was flawed.  With tar I am 
able to backup the 5.4783 GB of files in under two minutes.  I ran the Amanda 
"fullback" backup with the new configuration...sitting front of the server with 
my watch in hand.  Because the holding disk is larger than my backup size, 
Amanda backed the job up to the holding disk before the tape drive started 
writing.  It took nine minutes to write to the holding disk. Then the tape 
started writing.  It took only about three minutes to go from holding disk to 
tape. 12 minutes total for 5.5 gigabytes.  It appears that the problem is not 
in the tape write speed, but what is happening on the server to prepare and 
backup the data for the holding disk.