thanks for your help. well you appear to be right as my first "scsi" tape drive on the last server was actually one of those sony ait IDE drives and its way way faster than this real scsi drive. its one of the ones that came with an old dell server.
thanks for trying to help but i think i have a workaround, it appears that every backup (i'm using cpio) just startes writing at the curent tape position, and it LOOKS like it just overwrites everything thats there. i just tested doing a backup (using /dev/st0 knowing it always rewinds the tape). i listed the tape contents to make sure it backed up, then i backup up another directory and listed the tape, only the most recent backup is showing. SO>>> ill test a bit more but this looks like the behavior im looking for so i wont need to erase the tape (with a separate command).
i think the dlt is 3mbps transfer rate and up to 6 with compression.