Burning large files on BD. Capacity confusion

I have a couple of large files I want to burn to an M-Disc 50G BD-R DL. Files are larger than 4G so I have to use UDFv3, if I am not mistaken. (Or split, which I am not especially keen on doing.) A graphical tool is not an option (no X on the server and those do a remarkably bad job on that anyway in my experience) so what I plan on doing is the following: 1. find the capacity of my medium with dvd+rw-mediainfo. 2. create a temporary file with dd if=/dev/zero of=/tmp/bd.udf bs=2048 count=n with n being an integer extracted from mediainfo's output. 3. create a UDF filesystem on that temp with mkudffs -b 2048 -l somelabel /tmp/bd.udf 4. mount it with mount -o loop -t udf /tmp/bd.udf ./mntpt 5. populate it with my files cp xyz* mntpt/ 6. unmount it umount ./mntpt 7. burn it with growisofs -Z /dev/dvd=/tmp/bd.udf -speed=5 Please correct me if this is not a good procedure. I'd be grateful for improvements. What really confuses me is the output of dvd+rw-mediainfo: INQUIRY: [PIONEER ][BD-RW BDR-UD03][1.11] GET [CURRENT] CONFIGURATION: Mounted Media: 41h, BD-R SRM Media ID: VERBAT/IMf Current Write Speed: 6.0x4495=26970KB/s Write Speed #0: 6.0x4495=26970KB/s Write Speed #1: 4.0x4495=17980KB/s Write Speed #2: 2.0x4495=8990KB/s Speed Descriptor#0: 00/24438783 R@6.0x4495=26970KB/s W@6.0x4495=26970KB/s Speed Descriptor#1: 00/24438783 R@4.0x4495=17980KB/s W@4.0x4495=17980KB/s Speed Descriptor#2: 00/24438783 R@2.0x4495=8990KB/s W@2.0x4495=8990KB/s :-[ READ BD SPARE INFORMATION failed with SK=5h/MEDIUM NOT FORMATTED]: Wrong medium type READ DISC INFORMATION: Disc status: blank Number of Sessions: 1 State of Last Session: empty "Next" Track: 1 Number of Tracks: 1 READ FORMAT CAPACITIES: unformatted: 24438784*2048=50050629632 00h(6000): 23652352*2048=48440016896 32h(0): 23652352*2048=48440016896 32h(0): 11200512*2048=22938648576 32h(0): 24307712*2048=49782194176 READ TRACK INFORMATION[#1]: Track State: invisible incremental Track Start Address: 0*2KB Next Writable Address: 0*2KB Free Blocks: 24438784*2KB Track Size: 24438784*2KB READ CAPACITY: 0*2048=0 Should I use the "unformatted" block count for the temp file? What does "32h(0)" etc. mean? Is it necessary to somehow account for error correction spare blocks or something...? In a first test I used unformatted block count - 1 (don't ask me why;) ) and writing ends with an error message (that I unfortunately didn't record). The disc was readable though and md5 sums were fine. Can someone point me to a definitve guide for writing BDs on the command line?