Backup of wallet.dat enough?

[jixapori]

I make a backup of wallet.dat and store it on 3 different online storage and on 3 different usb pendrives. In encrypted archives of course. Every month I check if the cloud services and pendrives are still functional and replace if needed. Do I have a perfect backup for once and forever?

Now suppose my harddrive gets 100% defunct. Are my coins safe?

Could I copy the wallet.dat back, re-download the block chain and I am done?

Or do I have to make backup of wallet.dat each time I receive some new coins?

[Obsi]

You should backup your important files regularly. If your wallet.dat backup is too old, you may end up missing transactions to new addresses.

[jixapori]

You should backup your important files regularly. If your wallet.dat backup is too old, you may end up missing transactions to new addresses.

Important file(s?): wallet.dat, end of list. Correct?

So I have two options:

- do not create new addresses
- make a new backup after creating new address

That's it?

[Deafboy]

There is a pool of addresses pre-created. You can adjust this number in config file. So you don't have to backup after every new address you use.
Yes, there is no need to backup anything else. If you have multiple backups of wallet.dat, you are 99.9% safe.

[Nyhm]

I think this is accurate (can the community please confirm):

Even if you do not tell bitcoin-qt to make a new address, it may do so (or, minimally, use addresses you are not aware of) for bookkeeping purposes, such as transaction change.

Therefore, regular backups are a good idea, even when you have not manually requested new addresses. I also have read that bitcoin-qt will generate new addresses to keep it's pool (as mentioned prior) full, which is another reason for regular backups.

[Mushoz]

By default, Bitcoin-qt creates and maintains an address pool of 100 unused addresses. If you backup your wallet.dat file, this pool will be backed up as well, since it's included in the file. Now there are multiple things that use up one address:

-Sending BTC. By sending BTC any change gets send back to you to a new address, which is selected from the pool.
-Creating a new receiving address. This will also select 1 address from the pool of 100 addresses.

As long as you haven't used up the entire pool of addresses, you backup is the only thing that's needed to get your coins. If you run out of those 100 addresses you need to create another backup, so that coins received on new addresses that weren't included in the original backup, are backed up to your new backup. It is possible to increase the size of address pool if you don't want to backup as often, but I'm not sure how. Maybe someone else could chime in?

Anyway, here's a more thorough explanation of what I've just said: https://en.bitcoin.it/wiki/Man_page#Why_must_users_back_up_their_wallets_every_100_actions.3F