1. Exporting directly to tape 
   
VOLSIZE should be < tape capacity 
% exp userid=system/manager full=y file=/dev/rmt/0m volsize=145M 
After EXP has written <VOLSIZE> to the tape, it will prompt for next:
Please mount the next volume and hit <ret> when you are done.

2. Exporting to tape via unix named pipes

Note: 'dd' for tape devices may need 'bs=8k' or  similar depending on tape
% mknod /tmp/exp_pipe p		            # Make the pipe
% dd if=/tmp/exp_pipe of=<tape device> &    # Write from pipe to tape
% exp file=/tmp/exp_pipe <other options>    # Export to the pipe  

3. Creating a compressed export file
% mknod /tmp/exp_pipe p                     # Make the pipe
% compress < /tmp/exp_pipe > export.dmp.Z & # Background compress
 exp file=/tmp/exp_pipe <other options>    # Export to the pipe
 
4. Export to several files
(Note: Not all platforms support the split "-b" option used here)
% mknod /tmp/exp_pipe p		           # Make the pipe
% cd /fs_with_25gig_freespace		   # Make sure disk has space
% split -b2047m < /tmp/exp_pipe &	      # Split input to 2Gb chunks
% exp user/passwd file=/tmp/exp_pipe full=y  # Export to the pipe
  
This will split the export into several files called 'xaa', 'xab', 'xac' all of size 2047Mb. These can be fed back into import thus:
% mknod /tmp/imp_pipe p                      # Make the pipe
% cd /fs_with_25gig_freespace		      
% cat xaa xab xac > /tmp/imp_pipe &	      # Put files into the pipe
% imp user/passwd file=/tmp/imp_pipe	      # And import

The 'man' page for split shows options to generate more meaningful file names.
 
WARNING: Some versions of 'split' are very poor performance wise.

5. Export >2GB
  Use the split example above 
  OR
  Export to a NAMED PIPE and use unix 'cat' or 'dd'
  to  copy from this to 
  a large file. The 'cat' or 'dd' command must
  support  64 bit write and
  read offsets. Use the reverse for import.