I just saw this message almost a month later
If you have not change the blocking factor and you are using the tar defaults you have:
512 bytes for a block
20 as blocking factor
Therefore each record is
512 x 20 = 10240 bytes
So do these steps:
# mt -f /dev/nst0 eod
or something similar, if you have many files in the tape you can navigate from beginning of the file to beginning of the file with
# mt -f /dev/nst0 fsf n
rewind take you to 0, the fsf 1 will take you to the first block of the second file and so forth.
# mt -f /dev/nst0 tell
this will tell you the record #
if it give you 5000 then
5000 x 10240 = 48.82 MB
What I do is I change the blocking factor (instead of default 20) to 2048. So now when I do <tell> the number reported is in MB because the size of one record is about 1MB.
In summary: I modified a little bit your tar command
# tar -b 2048 -cf /dev/nst0 /home
so now when the archive is finished just
#mt -f /dev/nst0 tell
and you will have the MB used
-=terry(Denver)=-