reading files from tape

I am trying to use ncopen to access data stored on an Exabyte 8mm tape drive 
(from a Sparc10 running 4.1.3) -

        int ncid;

        ncid = ncopen("/dev/rst1",NC_NOWRITE);

but ncopen returns an error (ncid = -1). Has anybody done this successfully?

Thanks in advance,

PS - If I copy the file over to the disk and then try using ncopen on that file,
it works! But some files are rather large (~130 Mb) and I don't have enough
disk space for them.