How to properly store wallet.dat

Hi all,

I use an offline install of Bitcoin Core to store my coins. The private key is therefore encrypted inside the wallet.dat file. To access the coins, someone (me included) needs both the wallet.dat file and the associated passphrase.

To maintain a two-layers security, I store the passphrase and the wallet.dat file at different places, so if someone gets possession of any of the two, my coins are still safe.

While the passphrase is just a string of characters and can easily be written down on a sheet of paper, the wallet.dat can only be stored on some kind of drive, like a USB stick.

Drives, however, have a limited lifetime and end up losing data when left alone for a long time.

Therefore, how can I properly store my wallet.dat. In 15 years or so, when I want to spend bitcoins, how can I guarantee that the drive I stored my wallet.dat on still works.

If I just copy my wallet.dat on a USB stick, chances are that this stick will be unreadable in 15 years.

Thank you for your advices.