Well, perhaps it is a bad device. A run of amflush CONFIG resulted in another failure:
Fri Apr 15 11:52:31 2016: thd-0x18bae00: taper: Quantum-Superloader3-LTO-V4: updating state Fri Apr 15 11:52:31 2016: thd-0x18bae00: taper: Amanda::Taper::Scan::traditional stage 2: scan for any reusable volume Fri Apr 15 11:52:31 2016: thd-0x18bae00: taper: Quantum-Superloader3-LTO-V4: too early for another 'status' invocation Fri Apr 15 11:52:31 2016: thd-0x18bae00: taper: Quantum-Superloader3-LTO-V4: loading next relative to 5: 6 Fri Apr 15 11:52:31 2016: thd-0x18bae00: taper: Quantum-Superloader3-LTO-V4: using drive 0 Fri Apr 15 11:52:31 2016: thd-0x18bae00: taper: Quantum-Superloader3-LTO-V4: unloading drive 0 Fri Apr 15 11:52:31 2016: thd-0x18bae00: taper: invoking /usr/sbin/mtx -f /dev/sg4 unload 5 0 Fri Apr 15 11:53:41 2016: thd-0x18bae00: taper: Quantum-Superloader3-LTO-V4: unload complete Fri Apr 15 11:53:41 2016: thd-0x18bae00: taper: invoking /usr/sbin/mtx -f /dev/sg4 load 6 0 Fri Apr 15 11:55:01 2016: thd-0x18bae00: taper: Quantum-Superloader3-LTO-V4: polling 'tape:/dev/nst0' to see if it's ready Fri Apr 15 11:55:04 2016: thd-0x18bae00: taper: Quantum-Superloader3-LTO-V4: setting current slot to 6 Fri Apr 15 11:55:04 2016: thd-0x18bae00: taper: Slot 6 with label campus-NGH874L4 is usable Fri Apr 15 11:55:04 2016: thd-0x18bae00: taper: Amanda::Taper::Scan::traditional result: 'campus-NGH874L4' on tape:/dev/nst0 slot 6, mode 2 Fri Apr 15 11:55:04 2016: thd-0x18bae00: taper: Amanda::Taper::Scribe preparing to write, part size 0, using LEOM (falling back to holding disk as cache) (splitter) (LEOM supported) Fri Apr 15 11:55:04 2016: thd-0x18bae00: taper: Starting <Xfer@0x1bbbf40 (<XferSourceHolding@0x1bd7010> -> <XferDestTaperSplitter@0x1bc00b0>)> Fri Apr 15 11:55:04 2016: thd-0x18bae00: taper: Final linkage: <XferSourceHolding@0x1bd7010> -(PULL_BUFFER)-> <XferElementGlue@0x1bc1000> -(PUSH_BUFFER)-> <XferDestTaperSplitter@0x1bc00b0> Fri Apr 15 11:55:09 2016: thd-0x18bae00: taper: Building type TAPESTART header of 32768-32768 bytes with name='campus-NGH874L4' disk='' dumplevel=0 and blocksize=32768 Fri Apr 15 11:55:11 2016: thd-0x18bae00: taper: Device tape:/dev/nst0 error = 'Error writing filemark: Input/output error' Fri Apr 15 11:55:11 2016: thd-0x18bae00: taper: Device tape:/dev/nst0 setting status flag(s): DEVICE_STATUS_DEVICE_ERROR, and DEVICE_STATUS_VOLUME_ERROR Fri Apr 15 11:55:27 2016: thd-0x18bae00: taper: tape campus-NGH874L4 kb 0 fm -1 [OK]