Back up to Blu-Ray on Linux

It seems there is a bit of confusion on how to properly burn a blu-ray disk on Linux.

I've looked at the following web pages on this topic:
http://www.troubleshooters.com/linux/blu-ray-backup.htm
http://allgood38.io/burn-bluray-data-disks-on-linux-minimize-coasters.html

but, if you read carefully, the solution to burning is found here:
http://fy.chalmers.se/~appro/linux/DVD+RW/Blu-ray/

The problem seems to be that the blu-ray standard allocates some of the disk to recovering from bad sectors. So if you burn a full 25GB UDF image to the disk you end up over-writing the space reserved for bad sector relocation and the image is incomplete and pretty much useless.

growisofs respects this and will format a blank BD-R with 256GB of space for relocation.

So all you need to do is create a UDF file system of the right size:
25GB - 256MB - 2 sectors for padding
or
25000000000 - (256000000 + 2 * 2048)
which comes out to:
24743995904 bytes

So just modify the instructions on the referenced pages to create the correct size UDF file system:
truncate -s 24743995904
and then follow the rest of the instructions.

I've done this to back up my music collection and it seems to work well. I create the UDF file system and then build an index of the file contents and their MD5 sums. You can use that to verify that the files are all intact.

To build an index of a UDF file system:
cd to the file system's mount point
find . -type f \! -name Index.md5 -a \! -name \*.par2 -exec md5sum "{}" \; > Index.md5

To verify the disk after burning:
cd to the disk image
md5sum --check Index.md5 | grep -v "OK$"
All the valid files get written out as lines ending in OK. So the result is any invalid files.