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. 

const IMergeTreeDataPart & part,
    const DiskPtr & disk,
    const String & path)
{
    const auto settings = getSettings();
    auto disk_type = disk->getType();
    if (!(disk->supportZeroCopyReplication() && settings->allow_remote_fs_zero_copy_replication))
        return nullptr;
    String replica = getSharedDataReplica(part, disk_type);
    
    if (replica.empty())
        return nullptr;
    return executeFetchShared(replica, part.name, disk, path);
}
String StorageReplicatedMergeTree::getSharedDataReplica(