tape overwrite.....................

[VishalNikiSharma]

Hi
I am using windows api for tape backup.......
I am trying to write information in the tape......
once i have stored data in the tape i try to overwrite(change) the some data.....
though the data is modify successfully but it also erases the data present after the modify data.....
so please suggest me how to acheive the modifications without erasing the data following the modified one.......................
is it allowed to overwrite in the tape?if no then what else we can do...............
thanks
Vishal

[emmenjay]

Hi Vishal

It is 10 years since I wrote any tape software, so my expertise is somewhat out of date. However from the sound of your problem, some things haven't changed :)

The write head of a tape drive erases the bit in front of it. On an old Exabyte drive (Video 8) it used to erase ~20MB in front of the write head.

The only way to rewrite bits of tape was to use a fixed (or at least predictable) file size and rewrite a whole file at a time.

write file 1
write eof
write file 2
write eof
write file 3
write eof
write eot (end of tape)
rewind
seek file 2
rewrite file 2
rewind

You've replaced file 2 without hurting 1 or 3.

I don't know how this would work with modern hardware. I suspect that if you have hardware compression turned on it won't work (physical file size != logical file size).

[VishalNikiSharma]

ok thanks emm
i will try it
vishal