diff --git a/src/rpc/layout/test.rs b/src/rpc/layout/test.rs
index bb072c97..88eb518e 100644
--- a/src/rpc/layout/test.rs
+++ b/src/rpc/layout/test.rs
@@ -34,8 +34,8 @@ fn check_against_naive(cl: &LayoutVersion) -> Result<bool, Error> {
 		zone_token.insert(z.clone(), 0);
 	}
 	for uuid in cl.nongateway_nodes() {
-		let z = cl.get_node_zone(&uuid)?;
-		let c = cl.get_node_capacity(&uuid).unwrap();
+		let z = cl.expect_get_node_zone(&uuid);
+		let c = cl.expect_get_node_capacity(&uuid);
 		zone_token.insert(
 			z.to_string(),
 			zone_token[z] + min(NB_PARTITIONS, (c / over_size) as usize),
diff --git a/src/rpc/layout/version.rs b/src/rpc/layout/version.rs
index 947fab56..cbfbee94 100644
--- a/src/rpc/layout/version.rs
+++ b/src/rpc/layout/version.rs
@@ -70,6 +70,14 @@ impl LayoutVersion {
 		}
 	}
 
+	/// Given a node uuids, this function returns the label of its zone if it has one
+	pub fn get_node_zone(&self, uuid: &Uuid) -> Option<&str> {
+		match self.node_role(uuid) {
+			Some(role) => Some(&role.zone),
+			_ => None,
+		}
+	}
+
 	/// Returns the number of partitions associated to this node in the ring
 	pub fn get_node_usage(&self, uuid: &Uuid) -> Result<usize, Error> {
 		for (i, id) in self.node_id_vec.iter().enumerate() {
@@ -129,28 +137,22 @@ impl LayoutVersion {
 
 	// ===================== internal information extractors ======================
 
-	/// Given a node uuids, this function returns the label of its zone
-	pub(crate) fn get_node_zone(&self, uuid: &Uuid) -> Result<&str, Error> {
-		match self.node_role(uuid) {
-			Some(role) => Ok(&role.zone),
-			_ => Err(Error::Message(
-				"The Uuid does not correspond to a node present in the cluster.".into(),
-			)),
-		}
-	}
-
-	fn expect_get_node_capacity(&self, uuid: &Uuid) -> u64 {
+	pub(crate) fn expect_get_node_capacity(&self, uuid: &Uuid) -> u64 {
 		self.get_node_capacity(&uuid)
 			.expect("non-gateway node with zero capacity")
 	}
 
+	pub(crate) fn expect_get_node_zone(&self, uuid: &Uuid) -> &str {
+		self.get_node_zone(&uuid).expect("node without a zone")
+	}
+
 	/// Returns the sum of capacities of non gateway nodes in the cluster
-	fn get_total_capacity(&self) -> Result<u64, Error> {
+	fn get_total_capacity(&self) -> u64 {
 		let mut total_capacity = 0;
 		for uuid in self.nongateway_nodes() {
 			total_capacity += self.expect_get_node_capacity(&uuid);
 		}
-		Ok(total_capacity)
+		total_capacity
 	}
 
 	/// Returns the effective value of the zone_redundancy parameter
@@ -227,10 +229,7 @@ impl LayoutVersion {
 			// Check that every partition is spread over at least zone_redundancy zones.
 			let zones_of_p = nodes_of_p
 				.iter()
-				.map(|n| {
-					self.get_node_zone(&self.node_id_vec[*n as usize])
-						.expect("Zone not found.")
-				})
+				.map(|n| self.expect_get_node_zone(&self.node_id_vec[*n as usize]))
 				.collect::<Vec<_>>();
 			if zones_of_p.iter().unique().count() < zone_redundancy {
 				return Err(format!(
@@ -516,7 +515,7 @@ impl LayoutVersion {
 		}
 
 		let mut s_down = 1;
-		let mut s_up = self.get_total_capacity()?;
+		let mut s_up = self.get_total_capacity();
 		while s_down + 1 < s_up {
 			g = self.generate_flow_graph(
 				(s_down + s_up) / 2,
@@ -586,7 +585,7 @@ impl LayoutVersion {
 		}
 		for n in 0..self.nongateway_nodes().len() {
 			let node_capacity = self.expect_get_node_capacity(&self.node_id_vec[n]);
-			let node_zone = zone_to_id[self.get_node_zone(&self.node_id_vec[n])?];
+			let node_zone = zone_to_id[self.expect_get_node_zone(&self.node_id_vec[n])];
 			g.add_edge(Vertex::N(n), Vertex::Sink, node_capacity / partition_size)?;
 			for p in 0..NB_PARTITIONS {
 				if !exclude_assoc.contains(&(p, n)) {
@@ -632,7 +631,7 @@ impl LayoutVersion {
 		// The algorithm is such that it will start with the flow that we just computed
 		// and find ameliorating paths from that.
 		for (p, n) in exclude_edge.iter() {
-			let node_zone = zone_to_id[self.get_node_zone(&self.node_id_vec[*n])?];
+			let node_zone = zone_to_id[self.expect_get_node_zone(&self.node_id_vec[*n])];
 			g.add_edge(Vertex::PZ(*p, node_zone), Vertex::N(*n), 1)?;
 		}
 		g.compute_maximal_flow()?;
@@ -652,7 +651,7 @@ impl LayoutVersion {
 		let mut cost = CostFunction::new();
 		for (p, assoc_p) in prev_assign.iter().enumerate() {
 			for n in assoc_p.iter() {
-				let node_zone = zone_to_id[self.get_node_zone(&self.node_id_vec[*n])?];
+				let node_zone = zone_to_id[self.expect_get_node_zone(&self.node_id_vec[*n])];
 				cost.insert((Vertex::PZ(p, node_zone), Vertex::N(*n)), -1);
 			}
 		}
@@ -707,7 +706,7 @@ impl LayoutVersion {
 		let mut msg = Message::new();
 
 		let used_cap = self.partition_size * NB_PARTITIONS as u64 * self.replication_factor as u64;
-		let total_cap = self.get_total_capacity()?;
+		let total_cap = self.get_total_capacity();
 		let percent_cap = 100.0 * (used_cap as f32) / (total_cap as f32);
 		msg.push(format!(
 			"Usable capacity / total cluster capacity:   {} / {} ({:.1} %)",
@@ -754,7 +753,7 @@ impl LayoutVersion {
 						let mut old_zones_of_p = Vec::<usize>::new();
 						for n in prev_assign[p].iter() {
 							old_zones_of_p
-								.push(zone_to_id[self.get_node_zone(&self.node_id_vec[*n])?]);
+								.push(zone_to_id[self.expect_get_node_zone(&self.node_id_vec[*n])]);
 						}
 						if !old_zones_of_p.contains(&z) {
 							new_partitions_zone[z] += 1;
@@ -796,7 +795,7 @@ impl LayoutVersion {
 		for z in 0..id_to_zone.len() {
 			let mut nodes_of_z = Vec::<usize>::new();
 			for n in 0..storing_nodes.len() {
-				if self.get_node_zone(&self.node_id_vec[n])? == id_to_zone[z] {
+				if self.expect_get_node_zone(&self.node_id_vec[n]) == id_to_zone[z] {
 					nodes_of_z.push(n);
 				}
 			}