Re: blu-ray recommendations?
- Date: Mon, 03 Dec 2018 18:04:37 +0100
- From: "Thomas Schmitt" <scdbackup@xxxxxxx>
- Subject: Re: blu-ray recommendations?
> they sail quite beautifully
Not to forget the intrinsic corner protection feature at the time
> It seems that CDs/DVDs seem to lose single blocks, while flash (sticks, etc)
> seem to fail catastrophically, in my experience at least.
One can squeeze out a lot of semi-bad sectors by using several reader
drives and keeping track of the sucessfully read data. Best is to avoid
the Linux block device drivers and and to rather talk to the drive by
SCSI commands. Additional MD5 checksums give certainty about success.
As for ageing: I cannot speak for the storage conditions of other people's
backups, but under conditions which are acceptable for central eurpeans
a duration of 15 years seems to be no systematic problem.
Backup CDs which verfied in 2001 do still verify today. My experience with
DVD dates back to 2004, BD back to 2008.
The typical risk with backups is that they don't verify immediately after
they were made or that they do not cover the files which were supposed
to be covered. So there should be bulk checksums but also a convenient
opportunity for checking whether the files are there and readable.
Best is to keep lots of old backups.
> Now there would be some utility for an error-correcting encoder
> as easy to use as gzip. Perusing the debian repos I do see some
> libraries made for that (reed-solomon and friends).
Reed-Solomon already serves on the hardware level of optical media.
If it fails, then not enough redundancy survived the physical mishaps.
Have a nice day :)