Backup on BD-R. Was: What pulls in the tray of my /dev/sr1 ?
Hi,
> I apologize for mailing you off-list
Well, i got it with these headers
To: debian-user@lists.debian.org
Resent-From: debian-user@lists.debian.org
The mail address scdbackup@gmx.net is public for support of
optical drives, ISO 9660, and backup in general. If your topic
is of public interest in this field, you may also write to
bug-xorriso@gnu.org .
But i'd say that backup on BD is on topic for debian-user, too.
> I have a BD-R drive and a few disks that I would like to use for
> backups, and was wondering what your thoughts are on the safety of this
Single session on BD-R is at least as reliable as on
DVD-R or DVD+R. Multi-session has its limitations. Depending
on the drive one may only write about 120 sessions.
My youngest BD drive (LG BH16NS40, 20 months old) meanwhile
reliably spoils the fourth or fifth session of a BD-R. In the
past it did up to 130 sessions.
You have to be aware that old BD burners might be unable
to write to new BD-R media. Whatever, if the burn run succeeds
without error and checkreading confirms this success, then
the burner should work fine with other media of the same
product generation.
When buying media, better stay away from BD-R labeled as "LTH"
(Low-To-High reflectivity change on burning). They are likely
to be not readable by many drives.
> What about R vs RW disks,
It's BD-RE, not BD-RW. Their reliability is good.
Speed is a bit low, especially if the hardware Defect Management
stays enabled. This feature checkreads immediately after writing
a buffer-full of data. If the read quality is poor, then it
retries writing. If still bad, then it writes to the Spare Area
and the affected block addresses get redirected there.
BD-R can be formatted to perform Defect Management, too.
I prefer to use them without and to rather apply my own
checkreading after the burn run is finished.
> and what file system should I choose?
I use ISO 9660 with extensions RockRidge (for POSIX
attributes) and AAIP (for ACL and xattr).
With BD-R it must be a sequential write-once filesystem like
ISO 9660, sequential UDF, or a sequential archiver format
like tar or cpio.
You may also bring up a read-write filesystem in an image
file on hard disk and burn it to BD when its content is
complete.
With BD-RE you may use read-write filesystems like FAT or
ext{2,3,4}. Performance is sluggish because of Defect Management
and because of poor random-access addressing performance.
Expect not more than 2 or 3 MB/s of write throughput on
a 2x BD-RE (2xBD = 9 MB/s nominally).
I use BD-R and BD-RE for multi-volume backups with scdbackup,
and for multi-session backups with xorriso directly.
scdbackup
http://scdbackup.sourceforge.net/main_eng.html
splits large backup areas into file collections which
fit on single media:
sdvdbackup -bd /my/fat/tree
It can use xorriso or genisoimage for production of ISO 9660,
and growisofs, cdrskin, or xorriso for burning.
Checkreading by
time sdvdbackup_verify /dev/sr0 -auto_end
This software needs some initial configuration
http://scdbackup.sourceforge.net/examples.html#configure_dvd
(BD counts as DVD in this context. You will get disabled
Defect Management for all blocks after the first 100 MB.)
xorriso can read the ISO 9660 directory tree on BD, determine
the differences to file trees on hard disk, and burn an
add-on session which brings those differences into the
ISO 9660 filesystem.
See man xorriso, example "Incremental backup of a few
directory trees". (One should maintain such a command in
a shell script for easy repetition and for adding detail
improvements.)
Defect Management can be disabled after the first 100 MB
by command
-stream_recording 100m
(Or by -stream_recording "off" for total disabling.)
I leave Defect Management on for the first 100 MB because
the superblock and the directory tree usually fit into
this range. Bad file content is easier to handle than
bad metadata.
(The overall benefit of Defect Management is quite limited.
If the medium is really bad, then it will fail earlier than
without Defect Management. After much clonking and blinking.)
------------------------------------------------------------
scdbackup is not available as Debian package, because
of its peculiar configuration.
http://scdbackup.sourceforge.net/scdbackup-0.9.2.tar.gz
See
http://scdbackup.sourceforge.net/README
(or the README file in the tarball), chapters "Planning"
and "Installation".
xorriso is available in an old but sufficient version on Debian:
apt-get install xorriso
or in its newest version as source tarball from
http://www.gnu.org/software/xorriso/#download
which depends only on vanilla equipment for software development
and system runtime. I.e. gcc, ld, libc, libpthread.
(Current tarball is
http://www.gnu.org/software/xorriso/xorriso-1.4.0.tar.gz
)
------------------------------------------------------------
> hope you would give me
> some quick insights as one who knows these things. :)
I think i failed to comply to the wish about "quick".
Have a nice day :)
Thomas
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