This is my back up script I use at home that uses dump on OpenBSD.  If you can figure out scsh, maybe it will help you.  Or if someone else reads scheme, maybe he or she will notice something I'm overlooking.  I find dump a little intimidating myself, or at least thinly documented, though this script does create a backup that I can see interactively with restore.  You probably want to ignore the dump level command line argument I allow, since I haven't thought through how that would work with the file name I write to yet (if you think about it, you'll see it wouldn't be a good idea to supply an argument other than 0 to my script). 

.I could not get dump command to use special devices, like wd0a and sd0a, yet; so, in order to make a system backup I had to use dump with -f option and files-to-dump, i.e, by specifying directories and file names. 

.For the previous reason, dump doesn't fit very well when it's necessary to exclude directories and files from the backup being done.  Beside that, dump is quite tape oriented, as a great number of options relate to manipulating tape media. 

.As an alternative, I believe dar - Disk ARchiver is a better solution, when doing disk based backups: it's supposed to be used with disks, not with tape media; it supports incremental backups, as dump; it provides proper options for including and/or excluding directories and files. 

.At this moment, I am trying to build a bootable cdrom that shoul provide #dar, using command #mklivecd; I believe this makes sense, for the situation which there is not a bootable NetBSD installation on the machine to restore (the worst case).