I would also add that when using optical discs for backup, M-Discs are probably preferable over conventional dye-based discs.

Wow, do they work with conventional recorders?

Only if they say "M-Disc" on it. Many consumer recorders, especially if made by LG, support writing to these discs.

No, but they work with conventional readers. You need a special laser to do the physical etching that they're doing.

Thanks for the hint, no, but I'll do that in the future. In the past I actually had the problem of errorneous blocks one or two times. Eventhough these were Noname Multisession CDs that lay too much in the sun. (The media actually turned yellowish). Never had this problem again, but I only use brand media which I put it into proper covers that don't get too much light.

But I'll use it in the future... (Not sure if that's of interest anymore, but I used TrueCrypt for business backups.)