Long term archiving - which brand of CDROM do you recommend?

[Helmut Jarausch]

Hi,

can anybody please give me some recommendations for long term archiving
of data.
Which brands are known to be usable for this?

Many thanks for some information,
Helmut.

[Thomas Schmitt]

Hi,

can anybody please give me some recommendations for long term archiving of
data.
Which brands are known to be usable for this?

Brands are not a reliable guideline, i fear. You can read different
manufacturer ids from media of the same brand, just bought a year
apart (or just a shop apart).
Even Verbatim has gone promiscuous meanwhile.

If you successfully checkread the archived media after writing,
then you have good chances for a long life of the archive.
You should of course re-check during that lifetime.
I would store at least two copies at different places and hope
that the second copy is still ok when the first one fails its
yearly test (or vice versa).
The more copies, the more hope.

My oldest (outdated) CD-RW backup is from 2003 and still passes
the yearly random sample test. (One out of 60 CDs is checkread.)

It will be convenient and more fool-proof if you store checksums
on the same medium which they shall guard.

Actually the optical media all have own checksums and error correction
which are used internally by the drive. I had two cases, though, were
DVD+RW media returned false data without error indication.
So an own MD5 or SHA-1 helps to make clear that the data are still
as they should be.

One may discuss whether the lower density of CD or the more
sophisticated checksums of DVD and BD are to prefer.
I would make the proposed copies on media of different manufacturer
and/or media type (e.g. DVD-R versus DVD+R).


Said this, my youngest BD burner bears a logo "M (swirl) DISC",
which means "Millenial Disc". This is DVD+R or BD-R with mineral dye.
http://en.wikipedia.org/wiki/M-DISC
The web shows positive and negative opinions.
One thing is certain: They are more expensive than other media
of the same capacity.

There are archive formats like RAR, which are prepared for the
loss of chunks of archive data.
http://en.wikipedia.org/wiki/RAR
Optical media are supposed to fail partially first. So there is hope
that in the beginning of deterioration, enough redundant intermixed
archive parts stay readable.


Have a nice day :)

Thomas

[Thomas Schmitt]

Hi,

i forgot to mention quality checkers like QPxTool

http://qpxtool.sourceforge.net/

or the MS-Windows programs which are shown as screenshots in
CD/DVD/BD discussion forums.


Have a nice day :)

Thomas

[Thomas Schmitt]

Hi,

I have an LG HL-DT-ST DVDRAM GH22NS40 drive.
It looks as if this drive isn't supported by qpxtool.

This is well possible and not the fault of QPxTool.
The needed info about internal error detection and correction
has to be retrieved by non-standard SCSI/MMC commands.
Some burner firmware producers implement such commands.
Some even seem to publish the specs. Others don't.

Worse: Burner manufacturers buy their firmware and core hardware
from each other and create a wild mix of drive names and features.

readcd reports that every sector is in error which I cannot believe.

If you can read some correct blocks from the medium, e.g. some
human readable text, then this assessment can hardly be true.

dvdisaster -s doesn't report any errors.

Is that the same as http://dvdisaster.net/en/howtos10.html ?
This looks like a checkread for success with the drive-media internal
checksums. I.e. whether the drive indicates read error and how
long it needs to deliver the requested blocks.
Long read time indicates difficulties and multiple read attempts.

To sum up, I'm confused.

That's why i propose to have own checksums apart from the drive-media
checksums.
My backup tool scdbackup records one MD5 for the whole ISO filesystem.
My burn backend xorriso records with -for_backup three MD5 for the ISO
session and one MD5 for each data file. The first session MD5 guards
the superblock, the second guards the directory tree, and the third
one guards the rest with all data file content.

dvdisaster seems to offer similar capabilities, with more emphasis on
error correction. (I would feel better with two independent volume copies
rather than with two redundancy augmented single copies of half the
payload size. But that's personal taste.)
In any case it should be able to tell you if your medium went bad.


Have a nice day :)

Thomas