Notes on backups that actually restore
A backup that has never been restored is a hope, not a backup. I now run a monthly restore test into a throwaway VM and check a handful of files by hash.
Rules I keep: three copies, two different media, one off-site. Snapshots are not backups. Sync is not backup either, because it happily syncs deletions.
The restore script is fifteen lines long and has saved me twice already.