Data directory – Bitcoin Wiki

Data directory

The data directory is the location where Bitcoin’s data files are stored, including the wallet data file.

Contents

Default Location

Windows

Go to Embark -> Run (or press WinKey+R) and run this:

Bitcoin’s data folder will open. For most users, this is the following locations:

“AppData” and “Application data” are hidden by default.

You can also store Bitcoin data files in any other drive or folder.

If you have already downloaded the data then you will have to budge the data to the fresh folder. If you want to store them in D:\BitcoinData then click on “Properties” of a shortcut to bitcoin-qt.exe and add -datadir=D:\BitcoinData at the end as an example:

Embark Bitcoin, now you will see all the files are created in the fresh data directory.

Linux

By default Bitcoin will put its data here:

You need to do a “ls -a” to see directories that commence with a dot.

If that’s not it, you can do a search like this:

By default Bitcoin will put its data here:

Directory Contents

Files

An overview of these is in files.md in the Bitcoin Core documentation.

  • .lock
    • Bitcoin data directory lock file
  • bitcoin.conf [optional]
    • Contains configuration options.
  • blkxxxx.dat [Versions prior to v0.8.0]
    • Contains concatenated raw blocks. Stored are actual Bitcoin blocks, in network format, dumped to disk raw.
  • blkindex.dat [Versions prior to v0.8.0]
    • Indexing information used with blkxxxx.dat
  • __db.xxx
    • Used by BDB
  • db.log
  • debug.log
    • Bitcoin’s verbose log file. Automatically trimmed from time to time.
  • wallet.dat
    • Storage for keys, transactions, metadata, and options. Please be sure to make backups of this file. It contains the keys necessary for spending your bitcoins.
  • addr.dat [Versions prior to v0.7.0]
    • Storage for ip addresses to make a reconnect lighter
  • peers.dat [Versions v0.7.0 and later]
    • Storage for peer information to make a reconnect lighter. This file uses a bitcoin-specific file format, unrelated to any database system [1] .
  • fee_estimates.dat [Versions v0.Ten.0 and later]
    • Statistics used to estimate fees and priorities. Saved just before program shutdown, and read in at startup.

The data, index and log files are used by Oracle Berkeley DB, the embedded key/value data store that Bitcoin uses.

database subdirectory

Contains BDB journaling files

testnet3 subdirectory

Contains testnet versions of these files (if running with -testnet)

blocks subdirectory

[v0.8 and above] Contains blockchain data.

  • blk*.dat
    • Stored are actual Bitcoin blocks, in network format, dumped to disk raw. They are only needed for re-scanning missing transactions in a wallet, reorganizing to a different part of the chain, and serving the block data to other knots that are synchronizing.
  • blocks/index subdirectory
    • [v0.8 and above] A LevelDB database that contains metadata about all known blocks, and where to find them on disk. Without this, finding a block would be very slow.

chainstate subdirectory

[v0.8 and above] A LevelDB database with a compact representation of all presently unspent transaction outputs and some metadata about the transactions they are from. The data here is necessary for validating fresh incoming blocks and transactions. It can theoretically be rebuilt from the block data (see the -reindex instruction line option), but this takes a rather long time. Without it, you could still theoretically do validation indeed, but it would mean a utter scan through the blocks (7 GB as of may 2013) for every output being spent.

locks subdirectory

[v0.8 and above] Contains “undo” data.

You can see blocks as ‘patches’ to the chain state (they consume some unspent outputs, and produce fresh ones), and see the undo data as switch sides patches. They are necessary for rolling back the chainstate, which is necessary in case of reorganizations.

Personally identifiable data [v0.8 and above]

This section may be of use to you if you wish to send a friend the blockchain, avoiding them a hefty download.

  • wallet.dat
    • Contains addresses and transactions linked to them. Please be sure to make backups of this file. It contains the keys necessary for spending your bitcoins. You should not transfer this file to any third party or they may be able to access your bitcoins.
  • db.log
    • May contain information pertaining to your wallet. It may be securely deleted.
  • debug.log
    • May contain IP addresses and transaction ID’s. It may be securely deleted.
  • database/ folder
    • This should only exist when bitcoin-qt is presently running. It contains information (BDB state) relating to your wallet.
  • peers.dat
    • Unknown whether this contains personally identifiable data. It may be securely deleted.

Other files and folders (blocks, blocks/index, chainstate) may be securely transferred/archived as they contain information pertaining only to the public blockchain.

Transferability

The database files in the “blocks” and “chainstate” directories are cross-platform, and can be copied inbetween different installations. These files, known collectively as a knot’s “block database”, represent all of the information downloaded by a knot during the syncing process. In other words, if you copy installation A’s block database into installation B, installation B will then have the same syncing percentage as installation A. This is usually far swifter than doing the normal initial sync over again. However, when you copy someone’s database in this way, you are trusting them absolutely. Bitcoin Core treats its block database files as 100% accurate and trustworthy, whereas during the normal initial sync it treats each block suggested by a peer as invalid until proven otherwise. If an attacker is able to modify your block database files, then they can do all sorts of evil things which could cause you to lose bitcoins. Therefore, you should only copy block databases from Bitcoin installations under your private control, and only over a secure connection.

Each knot has a unique block database, and all of the files are very connected. So if you copy just a few files from one installation’s “blocks” or “chainstate” directories into another installation, this will almost certainly cause the 2nd knot to crash or get stuck at some random point in the future. If you want to copy a block database from one installation to another, you have to delete the old database and copy all of the files at once. Both knots have to be shut down while copying.

Only the file with the highest number in the “blocks” directory is ever written to. The earlier files will never switch. Also, when these blk*.dat files are accessed, they are usually accessed in a very sequential manner. Therefore, it’s possible to symlink the “blocks” directory or some subset of the blk*.dat files individually onto a magnetic storage drive without much loss in spectacle (see Splitting the data directory), and if two installations begin out with identical block databases (due to the copying described previously), subsequent runs of rsync will be very efficient.

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