The blocks.log file is used by nodeos to persist irreversible blocks. This is the actual local copy of the immutable blockchain maintained by the node. The default location of the blocks.log file is in the data/blocks directory. However the default data directory can be overridden with the -d [ --data-dir ] option on the nodeos command line.
Other
blocks.log filesYou can also download a blocks.log file from third party providers.