Restoring a NAS backup when you actually need it
Backups that have never been restored are a hope, not a plan. Twice a year I pick a random folder, delete it from a scratch copy, and time how long it takes to get it back from the NAS.
What went wrong this time
The snapshot was fine. The problem was that I had forgotten which share held the older snapshots, and the web UI search is slow on a spinning array. Now there is a text file at the top of every share saying what it is and how long it is kept.
The checklist
Pick a folder, note its size, restore to a new location, compare with rsync -anc, write down the time. That is the whole drill.