problem with st driver using dd command on Ultrium 3 tape drive
 

Hello, we are evaluating RHEL5 Server (30-day), and have encountered a problem using the dd command on an LTO-3 variable-blocksize tape. This same problem is also happening on a CentOS 5.2 build.
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We are using a Quantum Ultrium 3 tape drive through an Adaptec AHA-3960D/AIC-7899A U160/m (rev01) PCI card.
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We do an "mt -f /dev/nst0 setblk 0" followed by a "(dd bs=100 count=1 && dd bs=692480 oflag=append) </dev/nst0 >tapedump.out" and the first 100-byte header is written to file but it errors out after that. The dd output says "reading 'standard input': device or resource busy" and there is no output from dmesg.
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If we do a regular "dd if=/dev/nst0 of=tapedump.out" it errors out from the beginning with "'/dev/nst0': Cannot allocate memory", writes the first 100-byte header and I get a dmesg output of "failed to read 692480 byte block with 512 byte transfer".
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I thought the "mt -f /dev/nst0 setblk 0" sets the device up for variable block size? I have read that I can set up the option to make the buffer bigger in the modprobe.conf (st buffer_kbs=1024) but my st device is built into the kernel. I've also tried entering "st=buffer_kbs:1024" within the prompt but that didn't help either.
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Please advice on how to make the st driver internal buffer bigger or if you have other options I could try. We will greatly appreciate any help you can provide. Thank you.