no appendable (end marker unreadable)

Hi,

I have a tape that has no appendable (end marker unreadable) in its property and I cannot use it for backup and I understand that I have to reformat this tape.

but this tape has some new data on it and I must keep them. so I muse duplicate it on other tape. we have a tape librery with one drive. the tape that must be duplicated sys this:

used capacity: 348 GB

Data: 650 GB.

I think to do a data Duplicate first the data must be writen to the Hard drive and then to a new tape. but my question is, how mauch free space on the Hard drive Do I need? does the Hard drive must have 348 GB free space or 650 GB free space?

Thanks