Find another distribution to test with. DEbian, it seems, won't readily accept the proprietary drivers. You could opt for fedora or slackware.
Redhat, if you want the support and are willing to pay for it, may be able to find you a solution.
I have a SUSE 10.1 LINUX PC with a DELL 120T DLT7000 autoloader connected via an Adaptec AHA2944UW SCSII PCI card (supports up to 40MB/second).
The drive is rated to 35GB uncompressed.
I normally backup around 13 - 15 GB per tape and never in compressed mode. The tar backup takes about 1 1/2 hours to complete. The verify read (directory file list only) take between 3 and 4 times as long to complete.
I am using new Fuji DLT Tape IV tapes.
I've tested this on several SUSE machines with similar interfaces and get equivalent results as well as with other DLT 7000 drives.
This seems extremely slow write and read given the stated transfer rate for DLT 7000 series drives of 5MB/second sustained.
Am I missing something on tar -t -v? Or is this a hardware issue?