Backup with TAR

[Oleg Green]

Hello !

Maybe somebody had this problem before too, or can suggest some other way to backup the data?
I have DDS backup tape 5GB with Linux 7.2, and I want to backup only /usr directory which is 8GB.

My steps:
crontab : 00 1 * * 2-6 tar cvzf /dev/st0 -X /b.skipfiles  /usr 1>/b.result 2>/b.error

b.skipfiles has two lines :
/usr/me
/usr/scripts

And error is:
[root@Linux1 /]# cat b.error
tar: Removing leading `/' from member names
tar (child): /dev/st0: Wrote only 0 of 10240 bytes
tar (child): Error is not recoverable: exiting now

Thanks for your help