how good is the data reliability with CD ROM and DVD RAM?

what is your experience? I recently disposed of a couple hundred DVD and CD backups I'd made. As mentioned in a previous comment, it's simply too impractical to store terabytes of information in 4.7GB segments, plus they take up a LOT of space. HDDs aren't the most reliable, but this is what I use now for that reason. I make sure to keep the previous backup in case something happens. I'll only use optical backups now with the most important data. Backblaze has some interesting stats regarding HDD reliability (they are a data center using thousands of drives running constantly): https://www.backblaze.com/blog/hard-drive-stats-for-q1-2018/ As noted previously, beyond storage conditions, disc longevity depends on the types of dyes used in the discs. Gold is supposed to be best. Early on, they experimented with a wide variety of dye types, and the silver dyes were least reliable, oxidizing in only about 10 years. The thing is, no media format is going to last forever. The only really reliable way of keeping data around is multiple backups and data migration. Basically, for your really important stuff, you'll want a couple of backups, stored in different geographical locations (one local, one on cloud works, too). You'll want to periodically refresh the backups by migrating the data onto fresh media. In the preservation business, the ideal is to refresh after the cost of storage media is 1/2 of the initial investment. So, if you paid $1 a GB for the initial storage media, you'll want to migrate once the new format is $0.50 a GB, and then again when it is $0.25 and so on. This way, the total cost is double what you initially invested. Of course, while the cost per GB might drop steadily, the total amount on a particular media format will increase as well, such that the $150 HDD you bought 5 years ago will have twice the storage for...$150. Definitely open to other suggestions.