nimbus-eth2/docs/the_nimbus_book/src/era-store.md

Era store

!!! warning This feature is currently in BETA! Nodes using era files may need to be resynced as the data format is not yet considered stable.

Era files are a long-term archival format for Ethereum data. They are used to provide an easy interchange medium that clients interested in deep ethereum history can use to recreate past states.

!!! tip For more information about era files, see this post.

Each era file contains the blocks of 8192 slots (~27 hours). Blocks in era files are considered finalized. Since the history no longer is subject to change, the files are suitable to be archived for long-term storage, history recreation and other uses, and can be shared using traditional mediums such as http and bittorrent.

Nimbus can both create and use era files as a starting point to regenerate past history as well as to serve blocks.

Importing era files

To import an era archive, place the files in a folder called era in the data directory:

# Go to the nimbus directory
cd build/data/shared_mainnet_0

# Create era directory
mkdir -p era

# Download era store from era provider
wget --no-parent  -A '*.era' -q --show-progress -nd -r -c https://provider/era

With the era files present, perform a trusted node sync to complete the import, possibly with --reindex in order to create an archive node.

Generating era files

To generate era files, you need to first build Nimbus from source and sync the node using full sync. A checkpoint-synced node can be used to generate era files from the checkpoint onwards.

After that, build the additional ncli_db tool:

make ncli_db

The era export tool works by reading an existing Nimbus database and creating an era store. Every time the tool is run, it will check the existing store and export any new data to it.

# Go to the data directory of nimbus (the directory passed to --data-dir)
cd build/data/shared_mainnet_0/

# Create a directory for the era store
mkdir -p era
cd era

# Launch the era export
../../../ncli_db exportEra --db:../db

The first time the export is run, full history is exported which may take some time. Subsequent runs will top up the era store with new blocks.

It is recommended to set up a cron job or a timer, and run the export command every hour - doing so will ensure that era files are created on a timely basis.

!!! tip You do not need to stop Nimbus to generate era files. It is however not recommended to run era file generation on a node that is also serving validators.

Sharing era files

Era files can be shared directly from the era folder using a web server, or simply by copying them to a new location.

Options

You can pass a custom era store location to Nimbus using --era-dir:

nimbus_beacon_node --era-dir:/path/to/era

!!! tip Multiple nimbus beacon node instances can share the same era store.