Thanks, Sergey.
I think I have understand what you said after reading manual and trying :)

2012/5/27 Sergey Poznyakoff <gray@gnu....>:
> CUI Hao <cuihao.leo@gmai...> ha escrit:
>
>> Sorry I didn't make it clear that test0.tar is the first full dump. So
>> test01.tar shouldn't be empty.
>> I want it to be the new full dump in place of test0.tar.
>
> That's why you need to use a clear snapshot file.
>
>> > When listing or extracting, snapshot file is not used, but it is
>> > required syntactically (because the -g option requires an argument).
>> I don't think so. It's because snapshot file is provided that tar will
>> delete files that should be deleted correctly,
>
> Tar does not use snapshot files when extracting.
>
> Regards,
> Sergey