BD-RE DL write failures

[James Finnall <James@Finnall.net>]

Hello,
I have been using xorriso for sometime now.  Recently the tar file
exceeded a single layer media and so I purchased double layer media.  I
have not been able get reliable burns on the double layer.  The media
was labeled "for Video".  So I found some Maxell that was labeled "for
Data" and ordered five of them.  Two have worked very well every time
for my 26 GByte tar file.  The other three discs have the same issue as
the earlier media.  I suspect the two that are working will eventually
give problems as the backup grows.

The format, erase, and burn processes all complete normally with no
issues or errors.  When I mount and attempt to read the tar file it
aborts with an error message.

The script I am using is what I wrote sometime back.

#/bin/sh
DAY=`date --date=yesterday +%a`
FILE_NAME=tmgemail_backup.tar.tgz
DEVICE=/dev/sr0
LOG=/home/data/backups/dvdlog.txt
umount $DEVICE
/usr/bin/xorriso -stream_recording on -outdev $DEVICE -joliet on \
   -blank as_needed -speed "-1" \
   -map /backup/$DAY/$FILE_NAME /tmgemail/$FILE_NAME &>$LOG
mount $DEVICE /backup/dvd &>>$LOG
tar -tzf /backup/dvd/*/* &>>$LOG
cmp -l /backup/dvd/*/* /backup/$DAY/$FILE_NAME &>>$LOG
umount $DEVICE

I recently added the last lines to attempt to verify if the file was
actually usable.  I also added the -speed "-1" option to attempt to
lower the write speed but it did not have any effect. With or without
the quotes. It still reports 2.1x speed.

Note: tmgemail is the name of the server.

Any suggestion on how to get a reliable burn?

Thank you,
James