[Bug-tar] Incomplete tape

[James Calfee]

We are writing a single uncompressed archive to tape.  This works fine 6
out of 7 times.  About once a week though the end of the tape is
incomplete.  

We are alerted by errors during the Verify pass:
...
Verify ./pmp/Order_MDDB_DRUG.pmp
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: /dev/st0: Cannot read: Input/output error
tar: Too many errors, quitting
...
This time, there were 5 small files or 3,156 unrecoverable bytes.

>mt setblk 0

Putting the drive into variable length block mode seems to fix the
problem.  I'm not sure why though.  The tape is in 512 block size by
default and tar should use 10240 bytes as a default.  I'm reading that
these values should be compatible.

This is tar 1.13.25.  I do not see any fixes or changes that would help
in newer releases.  Have I missed one?
http://www.gnu.org/software/tar/#releases

...defaults...
# mt status
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 512 bytes. Density code 0x26 (DDS-4 or QIC-4GB).
Soft error count since last status=0
General status bits on (41010000):
 BOT ONLINE IM_REP_EN