Ordinary database engine is deprecated but there is no simple mean to change database engine to Atomic for existing databases.

Possible options:
- ALTER DATABASE MODIFY ENGINE query.
- Flag that triggers migration at ClickHouse startup.

The latter should be easier to implement. 

{
    auto settings = getSettings();
    if (!part.data_part_storage || !part.isStoredOnDisk() || !settings->allow_remote_fs_zero_copy_replication)
        return;
    if (!part.data_part_storage->supportZeroCopyReplication())
        return;
    zkutil::ZooKeeperPtr zookeeper = tryGetZooKeeper();
    if (!zookeeper)
        return;
    String id = part.getUniqueId();
    boost::replace_all(id, "/", "_");
    Strings zc_zookeeper_paths = getZeroCopyPartPath(
        *getSettings(), part.data_part_storage->getDiskType(), getTableSharedID(),
        part.name, zookeeper_path);
    String path_to_set_hardlinked_files;
    NameSet hardlinks;
    if (hardlinked_files.has_value() && !hardlinked_files->hardlinks_from_source_part.empty())
    {
        path_to_set_hardlinked_files = getZeroCopyPartPath(
            *getSettings(), part.data_part_storage->getDiskType(), hardlinked_files->source_table_shared_id,
            hardlinked_files->source_part_name, zookeeper_path)[0];
        hardlinks = hardlinked_files->hardlinks_from_source_part;
    }
    for (const auto & zc_zookeeper_path : zc_zookeeper_paths)