[vinw]

> it's probably cheaper to buy a new 4 TB hard drive every month

The reason for blurays might be that he's following rule 2 of the 3-2-1 Backup Strategy. 3 backups, 2 different types of storage media, 1 copy off-site.

If your house is hit by lightning it could wipe all your magnetic and solid state drives, but optical discs would probably be ok.

[meatmanek]

Most definitions of the 3-2-1 rule count the original data as one of the 3 copies [1][2][3] and don't go as far as to specify that you should be diversified against literal medium type. (Most recommend an external drive or NAS for your second local copy)

The "my house was hit by lightning" case is covered pretty well by your 1 offsite backup.

1. https://www.acronis.com/en-us/articles/backup-rule/ 2. https://www.carbonite.com/blog/article/2016/01/what-is-3-2-1... 3. https://www.backblaze.com/blog/the-3-2-1-backup-strategy/