src/garage/secrets.rs

@@ -163,7 +163,7 @@ mod tests {
 			r#"
 			metadata_dir = "/tmp/garage/meta"
 			data_dir = "/tmp/garage/data"
-			replication_mode = "3"
+			replication_factor = 3
 			rpc_bind_addr = "[::]:3901"
 			rpc_secret_file = "{}"
 
@@ -185,7 +185,7 @@ mod tests {
 			r#"
 			metadata_dir = "/tmp/garage/meta"
 			data_dir = "/tmp/garage/data"
-			replication_mode = "3"
+			replication_factor = 3
 			rpc_bind_addr = "[::]:3901"
 			rpc_secret_file = "{}"
 			allow_world_readable_secrets = true
@@ -296,7 +296,7 @@ mod tests {
 			r#"
 			metadata_dir = "/tmp/garage/meta"
 			data_dir = "/tmp/garage/data"
-			replication_mode = "3"
+			replication_factor = 3
 			rpc_bind_addr = "[::]:3901"
 			rpc_secret= "dummy"
 			rpc_secret_file = "dummy"

src/garage/tests/common/garage.rs

@@ -54,7 +54,7 @@ metadata_dir = "{path}/meta"
 data_dir = "{path}/data"
 db_engine = "lmdb"
 
-replication_mode = "1"
+replication_factor = 1
 
 rpc_bind_addr = "127.0.0.1:{rpc_port}"
 rpc_public_addr = "127.0.0.1:{rpc_port}"

src/model/garage.rs

@@ -9,7 +9,7 @@ use garage_util::config::*;
 use garage_util::error::*;
 use garage_util::persister::PersisterShared;
 
-use garage_rpc::replication_mode::ReplicationMode;
+use garage_rpc::replication_mode::*;
 use garage_rpc::system::System;
 
 use garage_block::manager::*;
@@ -39,8 +39,8 @@ pub struct Garage {
 	/// The set of background variables that can be viewed/modified at runtime
 	pub bg_vars: vars::BgVars,
 
-	/// The replication mode of this cluster
+	/// The replication factor of this cluster
-	pub replication_mode: ReplicationMode,
+	pub replication_factor: ReplicationFactor,
 
 	/// The local database
 	pub db: db::Db,
@@ -222,27 +222,26 @@ impl Garage {
 		.and_then(|x| NetworkKey::from_slice(&x))
 		.ok_or_message("Invalid RPC secret key")?;
 
-		let replication_mode = ReplicationMode::parse(&config.replication_mode)
+		let (replication_factor, consistency_mode) = parse_replication_mode(&config)?;
-			.ok_or_message("Invalid replication_mode in config file.")?;
 
 		info!("Initialize background variable system...");
 		let mut bg_vars = vars::BgVars::new();
 
 		info!("Initialize membership management system...");
-		let system = System::new(network_key, replication_mode, &config)?;
+		let system = System::new(network_key, replication_factor, consistency_mode, &config)?;
 
 		let data_rep_param = TableShardedReplication {
 			system: system.clone(),
-			replication_factor: replication_mode.replication_factor(),
+			replication_factor: replication_factor.into(),
-			write_quorum: replication_mode.write_quorum(),
+			write_quorum: replication_factor.write_quorum(consistency_mode),
 			read_quorum: 1,
 		};
 
 		let meta_rep_param = TableShardedReplication {
 			system: system.clone(),
-			replication_factor: replication_mode.replication_factor(),
+			replication_factor: replication_factor.into(),
-			write_quorum: replication_mode.write_quorum(),
+			write_quorum: replication_factor.write_quorum(consistency_mode),
-			read_quorum: replication_mode.read_quorum(),
+			read_quorum: replication_factor.read_quorum(consistency_mode),
 		};
 
 		let control_rep_param = TableFullReplication {
@@ -338,7 +337,7 @@ impl Garage {
 		Ok(Arc::new(Self {
 			config,
 			bg_vars,
-			replication_mode,
+			replication_factor,
 			db,
 			system,
 			block_manager,

src/rpc/layout/helper.rs

@@ -7,7 +7,7 @@ use serde::{Deserialize, Serialize};
 use garage_util::data::*;
 
 use super::*;
-use crate::replication_mode::ReplicationMode;
+use crate::replication_mode::*;
 
 #[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq, Eq)]
 pub struct RpcLayoutDigest {
@@ -29,7 +29,8 @@ pub struct SyncLayoutDigest {
 }
 
 pub struct LayoutHelper {
-	replication_mode: ReplicationMode,
+	replication_factor: ReplicationFactor,
+	consistency_mode: ConsistencyMode,
 	layout: Option<LayoutHistory>,
 
 	// cached values
@@ -57,7 +58,8 @@ impl Deref for LayoutHelper {
 
 impl LayoutHelper {
 	pub fn new(
-		replication_mode: ReplicationMode,
+		replication_factor: ReplicationFactor,
+		consistency_mode: ConsistencyMode,
 		mut layout: LayoutHistory,
 		mut ack_lock: HashMap<u64, AtomicUsize>,
 	) -> Self {
@@ -66,7 +68,7 @@ impl LayoutHelper {
 		// correct and we have rapid access to important values such as
 		// the layout versions to use when reading to ensure consistency.
 
-		if !replication_mode.is_read_after_write_consistent() {
+		if consistency_mode != ConsistencyMode::Consistent {
 			// Fast path for when no consistency is required.
 			// In this case we only need to keep the last version of the layout,
 			// we don't care about coordinating stuff in the cluster.
@@ -103,7 +105,7 @@ impl LayoutHelper {
 		// This value is calculated using quorums to allow progress even
 		// if not all nodes have successfully completed a sync.
 		let sync_map_min =
-			layout.calculate_sync_map_min_with_quorum(replication_mode, &all_nongateway_nodes);
+			layout.calculate_sync_map_min_with_quorum(replication_factor, &all_nongateway_nodes);
 
 		let trackers_hash = layout.calculate_trackers_hash();
 		let staging_hash = layout.calculate_staging_hash();
@@ -114,7 +116,8 @@ impl LayoutHelper {
 			.or_insert(AtomicUsize::new(0));
 
 		LayoutHelper {
-			replication_mode,
+			replication_factor,
+			consistency_mode,
 			layout: Some(layout),
 			ack_map_min,
 			sync_map_min,
@@ -139,7 +142,8 @@ impl LayoutHelper {
 		let changed = f(self.layout.as_mut().unwrap());
 		if changed {
 			*self = Self::new(
-				self.replication_mode,
+				self.replication_factor,
+				self.consistency_mode,
 				self.layout.take().unwrap(),
 				std::mem::take(&mut self.ack_lock),
 			);

src/rpc/layout/history.rs

@@ -6,11 +6,11 @@ use garage_util::encode::nonversioned_encode;
 use garage_util::error::*;
 
 use super::*;
-use crate::replication_mode::ReplicationMode;
+use crate::replication_mode::*;
 
 impl LayoutHistory {
-	pub fn new(replication_factor: usize) -> Self {
+	pub fn new(replication_factor: ReplicationFactor) -> Self {
-		let version = LayoutVersion::new(replication_factor);
+		let version = LayoutVersion::new(replication_factor.into());
 
 		let staging = LayoutStaging {
 			parameters: Lww::<LayoutParameters>::new(version.parameters),
@@ -119,7 +119,7 @@ impl LayoutHistory {
 
 	pub(crate) fn calculate_sync_map_min_with_quorum(
 		&self,
-		replication_mode: ReplicationMode,
+		replication_factor: ReplicationFactor,
 		all_nongateway_nodes: &[Uuid],
 	) -> u64 {
 		// This function calculates the minimum layout version from which
@@ -133,7 +133,7 @@ impl LayoutHistory {
 			return self.current().version;
 		}
 
-		let quorum = replication_mode.write_quorum();
+		let quorum = replication_factor.write_quorum(ConsistencyMode::Consistent);
 
 		let min_version = self.min_stored();
 		let global_min = self

src/rpc/layout/manager.rs

@@ -14,13 +14,13 @@ use garage_util::error::*;
 use garage_util::persister::Persister;
 
 use super::*;
-use crate::replication_mode::ReplicationMode;
+use crate::replication_mode::*;
 use crate::rpc_helper::*;
 use crate::system::*;
 
 pub struct LayoutManager {
 	node_id: Uuid,
-	replication_mode: ReplicationMode,
+	replication_factor: ReplicationFactor,
 	persist_cluster_layout: Persister<LayoutHistory>,
 
 	layout: Arc<RwLock<LayoutHelper>>,
@@ -38,20 +38,19 @@ impl LayoutManager {
 		node_id: NodeID,
 		system_endpoint: Arc<Endpoint<SystemRpc, System>>,
 		peering: Arc<PeeringManager>,
-		replication_mode: ReplicationMode,
+		replication_factor: ReplicationFactor,
+		consistency_mode: ConsistencyMode,
 	) -> Result<Arc<Self>, Error> {
-		let replication_factor = replication_mode.replication_factor();
-
 		let persist_cluster_layout: Persister<LayoutHistory> =
 			Persister::new(&config.metadata_dir, "cluster_layout");
 
 		let cluster_layout = match persist_cluster_layout.load() {
 			Ok(x) => {
-				if x.current().replication_factor != replication_mode.replication_factor() {
+				if x.current().replication_factor != replication_factor.replication_factor() {
 					return Err(Error::Message(format!(
 						"Prevous cluster layout has replication factor {}, which is different than the one specified in the config file ({}). The previous cluster layout can be purged, if you know what you are doing, simply by deleting the `cluster_layout` file in your metadata directory.",
 						x.current().replication_factor,
-						replication_factor
+						replication_factor.replication_factor()
 					)));
 				}
 				x
@@ -65,8 +64,12 @@ impl LayoutManager {
 			}
 		};
 
-		let mut cluster_layout =
+		let mut cluster_layout = LayoutHelper::new(
-			LayoutHelper::new(replication_mode, cluster_layout, Default::default());
+			replication_factor,
+			consistency_mode,
+			cluster_layout,
+			Default::default(),
+		);
 		cluster_layout.update_trackers(node_id.into());
 
 		let layout = Arc::new(RwLock::new(cluster_layout));
@@ -81,7 +84,7 @@ impl LayoutManager {
 
 		Ok(Arc::new(Self {
 			node_id: node_id.into(),
-			replication_mode,
+			replication_factor,
 			persist_cluster_layout,
 			layout,
 			change_notify,
@@ -295,11 +298,11 @@ impl LayoutManager {
 			adv.update_trackers
 		);
 
-		if adv.current().replication_factor != self.replication_mode.replication_factor() {
+		if adv.current().replication_factor != self.replication_factor.replication_factor() {
 			let msg = format!(
 				"Received a cluster layout from another node with replication factor {}, which is different from what we have in our configuration ({}). Discarding the cluster layout we received.",
 				adv.current().replication_factor,
-				self.replication_mode.replication_factor()
+				self.replication_factor.replication_factor()
 			);
 			error!("{}", msg);
 			return Err(Error::Message(msg));

src/rpc/layout/test.rs

@@ -5,6 +5,7 @@ use garage_util::crdt::Crdt;
 use garage_util::error::*;
 
 use crate::layout::*;
+use crate::replication_mode::ReplicationFactor;
 
 // This function checks that the partition size S computed is at least better than the
 // one given by a very naive algorithm. To do so, we try to run the naive algorithm
@@ -120,7 +121,7 @@ fn test_assignment() {
 	let mut node_capacity_vec = vec![4000, 1000, 2000];
 	let mut node_zone_vec = vec!["A", "B", "C"];
 
-	let mut cl = LayoutHistory::new(3);
+	let mut cl = LayoutHistory::new(ReplicationFactor::new(3).unwrap());
 	update_layout(&mut cl, &node_capacity_vec, &node_zone_vec, 3);
 	let v = cl.current().version;
 	let (mut cl, msg) = cl.apply_staged_changes(Some(v + 1)).unwrap();

src/rpc/replication_mode.rs

@@ -1,57 +1,94 @@
-#[derive(Clone, Copy)]
+use garage_util::config::Config;
-pub enum ReplicationMode {
+use garage_util::crdt::AutoCrdt;
-	None,
+use garage_util::error::*;
-	TwoWay,
+use serde::{Deserialize, Serialize};
-	TwoWayDangerous,
+
-	ThreeWay,
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
-	ThreeWayDegraded,
+#[serde(transparent)]
-	ThreeWayDangerous,
+pub struct ReplicationFactor(usize);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Default, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum ConsistencyMode {
+	/// Read- and Write-quorum are 1
+	Dangerous,
+	/// Read-quorum is 1
+	Degraded,
+	/// Read- and Write-quorum are determined for read-after-write-consistency
+	#[default]
+	Consistent,
 }
 
-impl ReplicationMode {
+impl ConsistencyMode {
-	pub fn parse(v: &str) -> Option<Self> {
+	pub fn parse(s: &str) -> Option<Self> {
-		match v {
+		serde_json::from_value(serde_json::Value::String(s.to_string())).ok()
-			"none" | "1" => Some(Self::None),
+	}
-			"2" => Some(Self::TwoWay),
+}
-			"2-dangerous" => Some(Self::TwoWayDangerous),
+
-			"3" => Some(Self::ThreeWay),
+impl AutoCrdt for ConsistencyMode {
-			"3-degraded" => Some(Self::ThreeWayDegraded),
+	const WARN_IF_DIFFERENT: bool = true;
-			"3-dangerous" => Some(Self::ThreeWayDangerous),
+}
-			_ => None,
+
+impl ReplicationFactor {
+	pub fn new(replication_factor: usize) -> Option<Self> {
+		if replication_factor < 1 {
+			None
+		} else {
+			Some(Self(replication_factor))
 		}
 	}
 
 	pub fn replication_factor(&self) -> usize {
-		match self {
+		self.0
-			Self::None => 1,
+	}
-			Self::TwoWay | Self::TwoWayDangerous => 2,
+
-			Self::ThreeWay | Self::ThreeWayDegraded | Self::ThreeWayDangerous => 3,
+	pub fn read_quorum(&self, consistency_mode: ConsistencyMode) -> usize {
+		match consistency_mode {
+			ConsistencyMode::Dangerous | ConsistencyMode::Degraded => 1,
+			ConsistencyMode::Consistent => self.replication_factor().div_ceil(2),
 		}
 	}
 
-	pub fn read_quorum(&self) -> usize {
+	pub fn write_quorum(&self, consistency_mode: ConsistencyMode) -> usize {
-		match self {
+		match consistency_mode {
-			Self::None => 1,
+			ConsistencyMode::Dangerous => 1,
-			Self::TwoWay | Self::TwoWayDangerous => 1,
+			ConsistencyMode::Degraded | ConsistencyMode::Consistent => {
-			Self::ThreeWay => 2,
+				(self.replication_factor() + 1) - self.read_quorum(ConsistencyMode::Consistent)
-			Self::ThreeWayDegraded | Self::ThreeWayDangerous => 1,
+			}
+		}
 	}
 }
 
-	pub fn write_quorum(&self) -> usize {
+impl std::convert::From<ReplicationFactor> for usize {
-		match self {
+	fn from(replication_factor: ReplicationFactor) -> usize {
-			Self::None => 1,
+		replication_factor.0
-			Self::TwoWay => 2,
-			Self::TwoWayDangerous => 1,
-			Self::ThreeWay | Self::ThreeWayDegraded => 2,
-			Self::ThreeWayDangerous => 1,
 	}
 }
 
-	pub fn is_read_after_write_consistent(&self) -> bool {
+pub fn parse_replication_mode(
-		match self {
+	config: &Config,
-			Self::None | Self::TwoWay | Self::ThreeWay => true,
+) -> Result<(ReplicationFactor, ConsistencyMode), Error> {
-			_ => false,
+	match (&config.replication_mode, config.replication_factor, config.consistency_mode.as_str()) {
-		}
+        (Some(replication_mode), None, "consistent") => {
+            tracing::warn!("Legacy config option replication_mode in use. Please migrate to replication_factor and consistency_mode");
+            let parsed_replication_mode = match replication_mode.as_str() {
+                "1" | "none"  => Some((ReplicationFactor(1), ConsistencyMode::Consistent)),
+                "2"           => Some((ReplicationFactor(2), ConsistencyMode::Consistent)),
+                "2-dangerous" => Some((ReplicationFactor(2), ConsistencyMode::Dangerous)),
+                "3"           => Some((ReplicationFactor(3), ConsistencyMode::Consistent)),
+                "3-degraded"  => Some((ReplicationFactor(3), ConsistencyMode::Degraded)),
+                "3-dangerous" => Some((ReplicationFactor(3), ConsistencyMode::Dangerous)),
+                _ => None,
+            };
+            Some(parsed_replication_mode.ok_or_message("Invalid replication_mode in config file.")?)
+        },
+        (None, Some(replication_factor), consistency_mode) => {
+            let replication_factor = ReplicationFactor::new(replication_factor)
+                .ok_or_message("Invalid replication_factor in config file.")?;
+            let consistency_mode = ConsistencyMode::parse(consistency_mode)
+                .ok_or_message("Invalid consistency_mode in config file.")?;
+            Some((replication_factor, consistency_mode))
         }
+        _ => None,
+    }.ok_or_message("Either the legacy replication_mode or replication_level and consistency_mode can be set, not both.")
 }

src/rpc/system.rs

@@ -112,8 +112,7 @@ pub struct System {
 
 	metrics: ArcSwapOption<SystemMetrics>,
 
-	replication_mode: ReplicationMode,
+	pub(crate) replication_factor: ReplicationFactor,
-	pub(crate) replication_factor: usize,
 
 	/// Path to metadata directory
 	pub metadata_dir: PathBuf,
@@ -243,7 +242,8 @@ impl System {
 	/// Create this node's membership manager
 	pub fn new(
 		network_key: NetworkKey,
-		replication_mode: ReplicationMode,
+		replication_factor: ReplicationFactor,
+		consistency_mode: ConsistencyMode,
 		config: &Config,
 	) -> Result<Arc<Self>, Error> {
 		// ---- setup netapp RPC protocol ----
@@ -274,14 +274,13 @@ impl System {
 		let persist_peer_list = Persister::new(&config.metadata_dir, "peer_list");
 
 		// ---- setup cluster layout and layout manager ----
-		let replication_factor = replication_mode.replication_factor();
-
 		let layout_manager = LayoutManager::new(
 			config,
 			netapp.id,
 			system_endpoint.clone(),
 			peering.clone(),
-			replication_mode,
+			replication_factor,
+			consistency_mode,
 		)?;
 
 		let mut local_status = NodeStatus::initial(replication_factor, &layout_manager);
@@ -315,7 +314,6 @@ impl System {
 			netapp: netapp.clone(),
 			peering: peering.clone(),
 			system_endpoint,
-			replication_mode,
 			replication_factor,
 			rpc_listen_addr: config.rpc_bind_addr,
 			rpc_public_addr,
@@ -427,7 +425,9 @@ impl System {
 	}
 
 	pub fn health(&self) -> ClusterHealth {
-		let quorum = self.replication_mode.write_quorum();
+		let quorum = self
+			.replication_factor
+			.write_quorum(ConsistencyMode::Consistent);
 
 		// Gather information about running nodes.
 		// Technically, `nodes` contains currently running nodes, as well
@@ -631,7 +631,7 @@ impl System {
 				.count();
 
 			let not_configured = self.cluster_layout().check().is_err();
-			let no_peers = n_connected < self.replication_factor;
+			let no_peers = n_connected < self.replication_factor.into();
 			let expected_n_nodes = self.cluster_layout().all_nodes().len();
 			let bad_peers = n_connected != expected_n_nodes;
 
@@ -774,14 +774,14 @@ impl EndpointHandler<SystemRpc> for System {
 }
 
 impl NodeStatus {
-	fn initial(replication_factor: usize, layout_manager: &LayoutManager) -> Self {
+	fn initial(replication_factor: ReplicationFactor, layout_manager: &LayoutManager) -> Self {
 		NodeStatus {
 			hostname: Some(
 				gethostname::gethostname()
 					.into_string()
 					.unwrap_or_else(|_| "<invalid utf-8>".to_string()),
 			),
-			replication_factor,
+			replication_factor: replication_factor.into(),
 			layout_digest: layout_manager.layout().digest(),
 			meta_disk_avail: None,
 			data_disk_avail: None,

src/rpc/system_metrics.rs

@@ -68,7 +68,7 @@ impl SystemMetrics {
 				let replication_factor = system.replication_factor;
 				meter
 					.u64_value_observer("garage_replication_factor", move |observer| {
-						observer.observe(replication_factor as u64, &[])
+						observer.observe(replication_factor.replication_factor() as u64, &[])
 					})
 					.with_description("Garage replication factor setting")
 					.init()

src/util/config.rs

@@ -30,12 +30,20 @@ pub struct Config {
 	)]
 	pub block_size: usize,
 
-	/// Replication mode. Supported values:
+	/// Number of replicas. Can be any positive integer, but uneven numbers are more favorable.
-	/// - none, 1 -> no replication
+	/// - 1 for single-node clusters, or to disable replication
-	/// - 2 -> 2-way replication
+	/// - 3 is the recommended and supported setting.
-	/// - 3 -> 3-way replication
+	#[serde(default)]
-	// (we can add more aliases for this later)
+	pub replication_factor: Option<usize>,
-	pub replication_mode: String,
+
+	/// Consistency mode for all for requests through this node
+	/// - Degraded -> Disable read quorum
+	/// - Dangerous -> Disable read and write quorum
+	#[serde(default = "default_consistency_mode")]
+	pub consistency_mode: String,
+
+	/// Legacy option
+	pub replication_mode: Option<String>,
 
 	/// Zstd compression level used on data blocks
 	#[serde(
@@ -244,10 +252,15 @@ fn default_sled_cache_capacity() -> usize {
 fn default_sled_flush_every_ms() -> u64 {
 	2000
 }
+
 fn default_block_size() -> usize {
 	1048576
 }
 
+fn default_consistency_mode() -> String {
+	"consistent".into()
+}
+
 fn default_compression() -> Option<i32> {
 	Some(1)
 }
@@ -359,7 +372,7 @@ mod tests {
 			r#"
 			metadata_dir = "/tmp/garage/meta"
 			data_dir = "/tmp/garage/data"
-			replication_mode = "3"
+			replication_factor = 3
 			rpc_bind_addr = "[::]:3901"
 			rpc_secret = "foo"