src/block/layout.rs

@@ -252,6 +252,14 @@ impl DataLayout {
 		path.push(hex::encode(&hash.as_slice()[1..2]));
 		path
 	}
+
+	pub(crate) fn without_secondary_locations(&self) -> Self {
+		Self {
+			data_dirs: self.data_dirs.clone(),
+			part_prim: self.part_prim.clone(),
+			part_sec: self.part_sec.iter().map(|_| vec![]).collect::<Vec<_>>(),
+		}
+	}
 }
 
 impl InitialFormat for DataLayout {

src/block/manager.rs

@@ -3,7 +3,7 @@ use std::pin::Pin;
 use std::sync::Arc;
 use std::time::Duration;
 
-use arc_swap::ArcSwapOption;
+use arc_swap::{ArcSwap, ArcSwapOption};
 use async_trait::async_trait;
 use bytes::Bytes;
 use rand::prelude::*;
@@ -83,7 +83,9 @@ pub struct BlockManager {
 	/// Directory/ies in which block are stored
 	pub data_dir: DataDirEnum,
 	/// Data layout
-	pub(crate) data_layout: DataLayout,
+	pub(crate) data_layout: ArcSwap<DataLayout>,
+	/// Data layout persister
+	pub(crate) data_layout_persister: Persister<DataLayout>,
 
 	data_fsync: bool,
 	compression_level: Option<i32>,
@@ -129,9 +131,9 @@ impl BlockManager {
 		system: Arc<System>,
 	) -> Result<Arc<Self>, Error> {
 		// Load or compute layout, i.e. assignment of data blocks to the different data directories
-		let layout_persister: Persister<DataLayout> =
+		let data_layout_persister: Persister<DataLayout> =
 			Persister::new(&system.metadata_dir, "data_layout");
-		let data_layout = match layout_persister.load() {
+		let data_layout = match data_layout_persister.load() {
 			Ok(mut layout) => {
 				layout
 					.update(&data_dir)
@@ -140,7 +142,7 @@ impl BlockManager {
 			}
 			Err(_) => DataLayout::initialize(&data_dir).ok_or_message("invalid data_dir config")?,
 		};
-		layout_persister
+		data_layout_persister
 			.save(&data_layout)
 			.expect("cannot save data_layout");
 
@@ -168,7 +170,8 @@ impl BlockManager {
 		let block_manager = Arc::new(Self {
 			replication,
 			data_dir,
-			data_layout,
+			data_layout: ArcSwap::new(Arc::new(data_layout)),
+			data_layout_persister,
 			data_fsync,
 			compression_level,
 			mutation_lock: vec![(); MUTEX_COUNT]
@@ -606,9 +609,10 @@ impl BlockManager {
 
 	/// Find the path where a block is currently stored
 	pub(crate) async fn find_block(&self, hash: &Hash) -> Option<DataBlockPath> {
-		let dirs = Some(self.data_layout.primary_block_dir(hash))
+		let data_layout = self.data_layout.load_full();
+		let dirs = Some(data_layout.primary_block_dir(hash))
 			.into_iter()
-			.chain(self.data_layout.secondary_block_dirs(hash));
+			.chain(data_layout.secondary_block_dirs(hash));
 		let filename = hex::encode(hash.as_ref());
 
 		for dir in dirs {
@@ -682,7 +686,7 @@ impl BlockManagerLocked {
 		let compressed = data.is_compressed();
 		let data = data.inner_buffer();
 
-		let directory = mgr.data_layout.primary_block_dir(hash);
+		let directory = mgr.data_layout.load().primary_block_dir(hash);
 
 		let mut tgt_path = directory.clone();
 		tgt_path.push(hex::encode(hash));

src/block/repair.rs

@@ -518,6 +518,86 @@ impl Worker for ScrubWorker {
 	}
 }
 
+// ---- ---- ----
+// THIRD KIND OF REPAIR: REBALANCING DATA BLOCKS
+// between multiple storage locations.
+// This is a one-shot repair operation that can be launched,
+// checks everything, and then exits.
+// ---- ---- ----
+
+pub struct RebalanceWorker {
+	manager: Arc<BlockManager>,
+	block_iter: BlockStoreIterator,
+	moved: usize,
+	moved_bytes: usize,
+}
+
+impl RebalanceWorker {
+	pub fn new(manager: Arc<BlockManager>) -> Self {
+		let block_iter = BlockStoreIterator::new(&manager);
+		Self {
+			manager,
+			block_iter,
+			moved: 0,
+			moved_bytes: 0,
+		}
+	}
+}
+
+#[async_trait]
+impl Worker for RebalanceWorker {
+	fn name(&self) -> String {
+		"Block rebalance worker".into()
+	}
+
+	fn status(&self) -> WorkerStatus {
+		WorkerStatus {
+			progress: Some(format!("{:.2}%", self.block_iter.progress() * 100.)),
+			freeform: vec![
+				format!("Blocks moved: {}", self.moved),
+				format!("Bytes moved: {}", self.moved_bytes),
+			],
+			..Default::default()
+		}
+	}
+
+	async fn work(&mut self, _must_exit: &mut watch::Receiver<bool>) -> Result<WorkerState, Error> {
+		if let Some((path, hash)) = self.block_iter.next().await? {
+			let prim_loc = self.manager.data_layout.load().primary_block_dir(&hash);
+			if path.parent().expect("no parent?") != prim_loc {
+				// block is not in its primary location,
+				// move it there (reading and re-writing does the trick)
+				let data = self.manager.read_block(&hash).await?;
+				self.manager.write_block(&hash, &data).await?;
+				self.moved += 1;
+				self.moved_bytes += data.inner_buffer().len();
+			}
+			Ok(WorkerState::Busy)
+		} else {
+			// all blocks are in their primary location:
+			// - the ones we moved now are
+			// - the ones written in the meantime always were, because we only
+			//   write to primary locations
+			// so we can safely remove all secondary locations from the data layout
+			let new_layout = self
+				.manager
+				.data_layout
+				.load_full()
+				.without_secondary_locations();
+			self.manager
+				.data_layout_persister
+				.save_async(&new_layout)
+				.await?;
+			self.manager.data_layout.store(Arc::new(new_layout));
+			Ok(WorkerState::Done)
+		}
+	}
+
+	async fn wait_for_work(&mut self) -> WorkerState {
+		unreachable!()
+	}
+}
+
 // ---- ---- ----
 // UTILITY FOR ENUMERATING THE BLOCK STORE
 // ---- ---- ----
@@ -526,16 +606,16 @@ const PROGRESS_FP: u64 = 1_000_000_000;
 
 impl BlockStoreIterator {
 	fn new(manager: &BlockManager) -> Self {
-		let min_cap = manager
-			.data_layout
+		let data_layout = manager.data_layout.load_full();
+
+		let min_cap = data_layout
 			.data_dirs
 			.iter()
 			.filter_map(|x| x.capacity())
 			.min()
 			.unwrap_or(0);
 
-		let sum_cap = manager
-			.data_layout
+		let sum_cap = data_layout
 			.data_dirs
 			.iter()
 			.map(|x| x.capacity().unwrap_or(min_cap /* approximation */))
@@ -543,7 +623,7 @@ impl BlockStoreIterator {
 
 		let mut cum_cap = 0;
 		let mut todo = vec![];
-		for dir in manager.data_layout.data_dirs.iter() {
+		for dir in data_layout.data_dirs.iter() {
 			let cap = match dir.state {
 				DataDirState::Active { capacity } => capacity,
 				_ => min_cap,

src/garage/cli/structs.rs

@@ -471,6 +471,9 @@ pub enum RepairWhat {
 		#[structopt(subcommand)]
 		cmd: ScrubCmd,
 	},
+	/// Rebalance data blocks among storage locations
+	#[structopt(name = "rebalance", version = garage_version())]
+	Rebalance,
 }
 
 #[derive(Serialize, Deserialize, StructOpt, Debug, Eq, PartialEq, Clone)]

src/garage/repair/online.rs

@@ -70,6 +70,12 @@ pub async fn launch_online_repair(
 			info!("Sending command to scrub worker: {:?}", cmd);
 			garage.block_manager.send_scrub_command(cmd).await?;
 		}
+		RepairWhat::Rebalance => {
+			info!("Rebalancing the stored blocks among storage locations");
+			bg.spawn_worker(garage_block::repair::RebalanceWorker::new(
+				garage.block_manager.clone(),
+			));
+		}
 	}
 	Ok(())
 }