Hi,
One thing you can do is as follows:-
in your backup script , you list the filesystems in size order , if your tape capcity is 4GB and you for example backup 3 filesystems the first being 2GB , next 1GB and final one 2.5 GB you can deduct the fileystems to backup
by total ( i.e. tape drive capcity )
Total 4GB
1stFS = 2GB
check :-
4GB - 1stFS(2GB) = 2GB
is 4GB > 2GB
back up fileystem "2GB left"
2ndFS= 1GB
is 2GB > 1GB
check 2GB - 2ndFS = 1GB
backit up ( 1GB left)
3rdFS = 2GB
is 1GB > 3rdFS(2GB)
no please insert a new tape
backitup
This way your script will calculate the size of filesystems
and don't have to worry about the size of filesystems
OR
Have a data file for filesystems that would fit onto tape
e.g. data file1 3 fileystems totalling 3.5GB , 2nd data
file listing 5 fileystems totaling 4GB , 3rd data file listing 2 fileystems totalling 2.5GB
and have a loop which reads each filesystem in your data files and backs them up and at the end of each one send a message out to insert a new tape , wait so many seconds/minutes and continue
OR
Have a look at tar flags to see if there is a flag to prompt for another tape , there may be freeware versions of tar programs that cater for this
HTH