Wallet backup strategy

[tenakha]

If I backup my wallet.dat file and store it somewhere safely. I can recover my wallet my installing bitcoin-qt and then dropping the existing wallet.dat file right?

My question is - do I need to back up after every few transactions? Or will my 'recovered' wallet automatically 'catch-up' ? As all transaction to-from my wallet *after* backing up are recorded in the ledger right? So I only have to do a one time backup?

Is that how it works?

[Gabi]

You need to update the backup if the wallet have new addresses. As long as the backup has all the addresses it's fine. But if you then create a new one and receive bitcoins in it, the backup wallet do NOT have it.

Your addresses=private keys. If you create a new address and you don't update the backup, then of course the backup don't have the key for that address

To complicate more the matter there is the fact that a newly created wallet.dat has already 100 address in it. 

[Meni Rosenfeld]

Your wallet file always has a buffer of 100 addresses. Meaning that as long as you haven't generated more than 100 addresses since you made the backup, you'll be fine.

You can assume that an address will be generated for every transaction you send or receive.

[BC12345]

Hi, I asked the same question on another sub forum and got the same answer as given by "Gabi". Could someone clarify some things for me, please:

- in another thread someone mentioned a bug that the 100 addresses are only created after a few transactions:

Really seems like the client should have an option to automatically backup the wallet after every transaction if this is the case ehh...

This thread is extremely old. Since then, we've implemented the creation of a pool of 100 (by default) pre-generated keys that your client will use. That means that a backup won't expire after each transaction anymore. However, you still need to do regular backups.

Note: there is currently a bug where the pool won't be created in a new wallet until a few transactions are made.

Is this bug fixed by now?

- If I click on the "New Address" button in the bitcoin client, will the client really create a "new" adress (and I have to update my backups) or will it use one of the 100 addresses in the buffer as long as there are some left?

- Is there a way to check how many of the 100 addresses are left?

[Meni Rosenfeld]

- in another thread someone mentioned a bug that the 100 addresses are only created after a few transactions:

Really seems like the client should have an option to automatically backup the wallet after every transaction if this is the case ehh...

This thread is extremely old. Since then, we've implemented the creation of a pool of 100 (by default) pre-generated keys that your client will use. That means that a backup won't expire after each transaction anymore. However, you still need to do regular backups.

Note: there is currently a bug where the pool won't be created in a new wallet until a few transactions are made.

Is this bug fixed by now?

This quote is over a year old and I haven't heard it in any recent context, so I'd say it's fixed.

- If I click on the "New Address" button in the bitcoin client, will the client really create a "new" adress (and I have to update my backups) or will it use one of the 100 addresses in the buffer as long as there are some left?

It will use an address from the buffer, and generate a new address to replenish it. The buffer will always have 100 addresses.

[BC12345]

Ok, thank you!

[AbsoluteZero]

I think you also have to back up the wallet if you send Coins.
Because the program might put the change In a New address.
Change could be the entire balance you have.

[BC12345]

I think you also have to back up the wallet if you send Coins.
Because the program might put the change In a New address.
Change could be the entire balance you have.

I do not think so. The way I understand it (from the answers above), the client creates a pool of 100 addresses that it uses to receive change from send transactions. I think you should update your backups if:

- you manually create a new address

- your bitcoins in your wallet are so scattered over your addresses that you can not safely assume that the change from a send transaction can be stored in an address that is already existing in your wallet

It would be nice if someone could confirm that my assumptions are correct or give some other advice for a good backup strategy. I think this is an important topic for someone who is new with bitcoins.

[Meni Rosenfeld]

It would be nice if someone could confirm that my assumptions are correct

Not really. The wallet has a pool of spare addresses. Whenever it needs a new address, whether a change address or when clicking the "new address" button, it takes one from the pool and replenishes it with a fresh one. A change address is always one which was never used before.

or give some other advice for a good backup strategy.

As mentioned, the backup is good until 100 new addresses are generated (change from sending + new recipients). The backup should be frequent enough that even under heavy usage you won't use 100 between backups, otherwise all coins could be lost.

[BC12345]

It would be nice if someone could confirm that my assumptions are correct

Not really. The wallet has a pool of spare addresses. Whenever it needs a new address, whether a change address or when clicking the "new address" button, it takes one from the pool and replenishes it with a fresh one. A change address is always one which was never used before.

or give some other advice for a good backup strategy.

As mentioned, the backup is good until 100 new addresses are generated (change from sending + new recipients). The backup should be frequent enough that even under heavy usage you won't use 100 between backups, otherwise all coins could be lost.

Ok, I did not know that. Again, thank you.