Many improvements on ring/replication and its configuration:

- Explicit "replication_mode" configuration parameters that takes
  either "none", "2" or "3" as values, instead of letting user configure
  replication factor themselves. These are presets whose corresponding
  replication/quorum values can be found in replication/mode.rs

- Explicit support for single-node and two-node deployments
  (number of nodes must be at least "replication_mode", with "none"
  we can have only one node)

- Ring is now stored much more compactly with 256*8 + n*32 bytes,
  instead of 256*32 bytes

- Support for gateway-only nodes that do not store data
  (these nodes still need a metadata_directory to store the list
  of bucket and keys since those are stored on all nodes; it also
  technically needs a data_directory to start but it will stay
  empty unless we have bugs)

1 files changed, 13 insertions, 8 deletions

diff --git a/src/model/garage.rs b/src/model/garage.rs
index 5c6c21f2..c3594934 100644
--- a/src/model/garage.rs
+++ b/src/model/garage.rs
@@ -7,6 +7,7 @@ use garage_rpc::membership::System;
 use garage_rpc::rpc_client::RpcHttpClient;
 use garage_rpc::rpc_server::RpcServer;
 
+use garage_table::replication::ReplicationMode;
 use garage_table::replication::TableFullReplication;
 use garage_table::replication::TableShardedReplication;
 use garage_table::*;
@@ -50,6 +51,9 @@ impl Garage {
 		background: Arc<BackgroundRunner>,
 		rpc_server: &mut RpcServer,
 	) -> Arc<Self> {
+		let replication_mode = ReplicationMode::parse(&config.replication_mode)
+			.expect("Invalid replication_mode in config file.");
+
 		info!("Initialize membership management system...");
 		let rpc_http_client = Arc::new(
 			RpcHttpClient::new(config.max_concurrent_rpc_requests, &config.rpc_tls)
@@ -60,32 +64,33 @@ impl Garage {
 			rpc_http_client,
 			background.clone(),
 			rpc_server,
+			replication_mode.replication_factor(),
 		);
 
 		let data_rep_param = TableShardedReplication {
 			system: system.clone(),
-			replication_factor: config.data_replication_factor,
-			write_quorum: (config.data_replication_factor + 1) / 2,
+			replication_factor: replication_mode.replication_factor(),
+			write_quorum: replication_mode.write_quorum(),
 			read_quorum: 1,
 		};
 
 		let meta_rep_param = TableShardedReplication {
 			system: system.clone(),
-			replication_factor: config.meta_replication_factor,
-			write_quorum: (config.meta_replication_factor + 1) / 2,
-			read_quorum: (config.meta_replication_factor + 1) / 2,
+			replication_factor: replication_mode.replication_factor(),
+			write_quorum: replication_mode.write_quorum(),
+			read_quorum: replication_mode.read_quorum(),
 		};
 
 		let control_rep_param = TableFullReplication {
 			system: system.clone(),
-			max_faults: config.control_write_max_faults,
+			max_faults: replication_mode.control_write_max_faults(),
 		};
 
 		info!("Initialize block manager...");
 		let block_manager = BlockManager::new(
 			&db,
 			config.data_dir.clone(),
-			data_rep_param.clone(),
+			data_rep_param,
 			system.clone(),
 			rpc_server,
 		);
@@ -95,7 +100,7 @@ impl Garage {
 			BlockRefTable {
 				block_manager: block_manager.clone(),
 			},
-			data_rep_param,
+			meta_rep_param.clone(),
 			system.clone(),
 			&db,
 			"block_ref".to_string(),