having multiple backup methods is better. Portable HDD as well as back-up services.

CD/DVD are not that good longterm, they need regular copies say 2 or 3 years but you may be accessing them regularly and they are portable. You can write on them, highlighting the retrieval methodology as equally important. It is all data until you get at it, then it is information.

If you are about to archive it is a good time to stop and consider the layout of the archive. Do you have a database with plenty of TAGs for cross reference etc? Checksums (in the database) on the files to indicate integrity? If the checksum disagrees with the file - there is an error in the file (or the storage of the checksum even).

Checksum generation is a trivial job in Excel to write the macro. I did it for spotting files that have changed so that I only upload those that change to my website - made it a quicker online process.