[Help-tar] --listed-incremental and tape full (tar 1.20 for now)

[Jakob Bohm]

Hi,

I am having a problem with the behavior of --listed-incremental when the 
tape of a single-volume archive fills up.

To avoid the backups on subsequent days becoming increasingly larger, I 
want the incremental index to list the files that were actually backed 
up before the tape was full.  However currently, I seem to get an index 
saying that nothing was backed up on the full tape (its uncompressed 
LTO-4 = 800Gio per tape).

I am wondering if there is a way to make this happen without too much 
difficulty.

One thing I have not tried (because it would create a multi-volume 
archive with the second and later volumes missing) would be to specify 
"--tape-length 800000000000 --info-script=/bin/false" however given the 
observed handling of tape full I would suspect that doing this would 
have the same result as a simple broken output pipe[2].

Hope someone can help with this.

J Bohm, Software Developer.


Additional notes:

1. This is on a Debian 5.0.x(Lenny) system with its corresponding 
version of GNU tar 1.20, but compiling another tar version to make 
things work would not be much of a problem.

2. I am piping the output from tar through a double-buffering program 
similar to the classic "buffer" program in order to reduce shoe-shining 
in the tape drive caused by the disk being slower than the tape.  The 
buffer is configured to buffer up about 792 MibiOctets of archive at a 
time, write lots of 100Kio tape blocks continuously in a burst at tape 
speed, then sleep until the buffer is full again.  Thus tape full 
technically manifests itself as a broken output pipe rather than a real 
disk full error code in case that makes any difference to tar.

3. This is a production system, I really need the backup to work 5 days 
a week, 52 weeks/year.  As each backup run may take up to 18 hours (2 
hours lead time + 1 minute/burst), I cannot do much full scale 
experimenting.

4. This is all done by a cron job, no human interaction possible.