Re: [Bug-xorriso] BDXL support

[Thomas Schmitt]

Hi,

Johan de Jong wrote:
> the current consensus is that degradation or organic dyes
> results in corruption in a few years or sometimes months

I have to disagree. Once written and verified, optical media
seem to stay readable for at least a decade.

I can still read my remaining CDs from 1999 and DVDs from 2004.
Burned by cdrecord and growisofs under control of scdbackup.
I began to record MD5s in 2003. So with older CDs i have to
rely on not getting an i/o error within the size of their
ISO filesystems.
My oldest BDs are from 2008. So their decade is not full yet.
Storage conditions: Dry, dark, about 15 to 35 Celsius.

More problematic is re-use of media which were stored for
years. 10 to 20 % loss is quite normal then. Media which get
re-written after a few months rarely fail on re-write.
This effect hits CD-RW, DVD+RW, and BD-RE alike.


> [future] optical drives hard to come by and the data needs
> to be migrated

I am very optimistic about future availability of reader hardware.
Data CDs are around since about 20 years and still readable by
all optical drives. My old 500 MB QIC tapes from the 1990s
lost their reader hardware ten years ago, when the Ultra SCSI
controllers had been pushed aside by IDE which already became
replaced by SATA. You need a complete old computer to read
such stuff.
With CD you just need to buy a drive that matches your current
computer.

If you use optical media for archiving and delete the original
data on hard disk, then you should have several identical copies
and checkread them once per year. As soon as the first copy
fails, make more copies of the still good ones.

If the optical media serve as backup, then have more than one
of them. Not necessarily identical ones.
If there are several incremental backup levels then especially
checkread the older ones from time to time. In case of decay,
make new updates from the level before the oldest bad level.


Have a nice day :)

Thomas