[sclug] Blu-Ray writing

[Graham Swallow]

On Mon, Jul 16, 2012 at 22:10:46 +0100, Daniel Craigie wrote:

: As the available capacity of my DroboPro steadily decreases I am
: going though a period of data paranoia.  Even with the dual failure
: redundancy provided by the disk robot, I have decided that a mass
: archive is required and that Blu-Ray is my best choice with the
: Dual Layer disks holding up to 50Gb a time.

Use 'find . -sixze ...' to find all files of size 4GB or more or 2K less
(but surely DVD uses a physical 32K block size and 2K logical?)
If you have a collection of .iso's you will want to test they md5sum OK.

(The note I saw doesnt make sense, as the .iso image will do all the
work, and the device will end up as one big image, with a 1 item TOC,
but the growisofs page mentions this)

I also vaguely recollect something about when multi-sessions straddle the
media-layer-edge, and also the 4G (of 4.7) line, which might be
paranoia, but you should google, grep and browse the sources,
and the support logs. I know thats exactly what you dont want to hear,
but you definitely want a comprehensive tree of checksums,
and a script that notices a missing entry. check dmesg
find . -type f -exec md5sum {} ';'  # or better script

http://fy.chalmers.se/~appro/linux/DVD+RW/Blu-ray/
is the home of growisofs, maybe someone else has patched it.
It calls the standard mkisofs, but uses its own device driver,
and sorts out multi-session parameters. I like it, but it is not as deep.

(I say device driver, the linux-scsi-generic is the device driver that
shuttles scsi-command-data-packets to and from the device,
the drive itself needs to be driven with its own variation on the mmc3
standard commands. A bit like AT-modems and serial line drivers.
I'm not sure what happens with /dev/sr0 as it is already different
from /dev/rmt0 but I think the application sends the correct scsi frames,
and needs a database of irregular behavior from odd devices -vs- spec)

cdrecord / cdrtools is the home of mkisofs/cdd2a/* and the well known
scsi-cd-burner. It has a reputation for being the oldest, best,
(pre-)SCSI driver, albeit slightly odd. Read its source comments.

There is also a project *somewhere* that write multiple copies of files,
on different places on the disk, or multiple disks, with error
correction codes, and claims to be able to recover from various sorts
of problems.

There are also sites about UDF which might have some hints.

Tangent:
To be honest, this 'big data' movement has always worried me,
maybe its the data-centre version of the credit crunch
.
We are buying into an ever growing dependency,
with grains of vital data lost in a sand-desert of extra stuff.

Tapes are not increasing in capacity to match disks,
optical media dont last, and thanks to that flood,
disk copies are still expensive, and even then you
have to wait for the gigabit transfer reload to complete.

Graham