Random Access Tape 2452

Let me throw a bit of cold water on this part of the thread. DDS drives write an END OF MEDIUM block after any data write. This comes after the FileMark that the operating system software also writes. The DDS drive firmware can not read beyond this END OF MEDIUM, no matter what software tricks you try, perhaps things you remember from your experience with 9-track tape.

It's relatively easy to lose your 2GB of backup data by writing a few kB at the beginning of the DDS tape. This sad experience is discussed occasionally in some net.news group or another.

Oh, by the way, DDS is the more correct name for the 4mm tape drives commonly called DAT. Back around 1980 +-2 there was a competing 4mm format called DATA-DAT. It didn't survive for very long.

Naturally, the EOM block is overwritten when a DDS tape is appended to. But another one is placed at the end of that write.

On the other hand, it is possible to parbreastion a DDS tape into two parbreastions that can be written independently. So you can have an index parbreastion at the begining of the tape, and write the real data on the second parbreastion. You can read more about this in the Linux man.page for mt(1), and probably elsewhere.

carl -- carl lowenstein marine physical lab u.c. san diego