Down side, requires writer that is M-Disk capabale, and disk are expensive (ie about 3 bucks per disk.
The problem with DVD disks is that the disk you create have anywheres from several thousand correctable errors -> a Hundred thousand correctable errors. Use to use Plextor Plextools and a Old Plextor DVD drive to measure different media, recorded at differnt speeds. Surprising at number of correctable errors. These "correctable" errors are much more likely to end up as UNcorrectable erros. The problem with "evaluations" (for DVD/BE/M-disK) is that the recording is done with a "HIGH" end writer with near 0 correctable errors.
PS: Nero CD speed will evaluate DVD errors for Some DVD drives (a few others drives the registry could be eddet to remove the "Blocked" entry.
Did not do any testing on Blu-ray created at home.
HDD. Have several 2 Gig SCSI disk (at the time HIGH end) manuf around 1998, used until 2004, stored from 2004 -> 2009. Most But not all survivied and two are STILL in use. The biggest problem I had is that the spindels did not want to start up - cured with a gental tap. But run of the Mill HDDs I would not expect much over 5 -> 10 years. The Magnetic domains are much more dense a susceptible to magnetic migration.
While that sounds promissing my take is if it is really that important, then:
.. Store on DVD/Bluray/M-disk and a copy onto a 2nd media source. and Verify both copies at least once per year.
.. For SSDs verify quarterly.
.. DVD/Blue ray, store sealed with a dessicant.
Also, what many seem to forget - You must still have a system to read what ever you use to store that data on, ie
will USB ports still exist, will SATA interface exist, may need to visit a musem to find a DVD drive in 20 years.
I have had very good luck with both DVD and Blue Ray disks. The key here is to buy good quality media and to store them properly. Multiple copies is a good idea in case there is an issue with one of the disks.