diff --git a/block-cache/copier.cc b/block-cache/copier.cc
new file mode 100644
index 0000000..60ca93b
--- /dev/null
+++ b/block-cache/copier.cc
@@ -0,0 +1,7 @@
+#include "block-cache/copier.h"
+
+//----------------------------------------------------------------
+
+
+
+//----------------------------------------------------------------
diff --git a/block-cache/copier.h b/block-cache/copier.h
new file mode 100644
index 0000000..41ed82e
--- /dev/null
+++ b/block-cache/copier.h
@@ -0,0 +1,30 @@
+#ifndef BLOCK_CACHE_COPIER_H
+#define BLOCK_CACHE_COPIER_H
+
+#include "block_cache.h"
+
+#include <string>
+
+//----------------------------------------------------------------
+
+namespace bcache {
+	class copier {
+	public:
+		// block size in sectors
+		copier(std::string const &src, std::string const &dest,
+		       unsigned block_size);
+		~copier();
+
+		// Returns the number of sectors copied
+		unsigned copy(block_address from, block_address to);
+
+		unsigned get_block_size() const;
+
+	private:
+		unsigned block_size_;
+	};
+}
+
+//----------------------------------------------------------------
+
+#endif
diff --git a/caching/cache_writeback.cc b/caching/cache_writeback.cc
index a3d27d1..042ae74 100644
--- a/caching/cache_writeback.cc
+++ b/caching/cache_writeback.cc
@@ -1,13 +1,16 @@
-#ifndef CACHING_CACHE_WRITEBACK_H
-#define CACHING_CACHE_WRITEBACK_H
-
+#include "persistent-data/file_utils.h"
+#include "block-cache/copier.h"
 #include "caching/commands.h"
+#include "caching/mapping_array.h"
+#include "caching/metadata.h"
 #include "version.h"
 
 #include <boost/optional.hpp>
 #include <getopt.h>
 #include <string>
+#include <stdexcept>
 
+using namespace bcache;
 using namespace caching;
 using namespace boost;
 using namespace std;
@@ -23,8 +26,117 @@ namespace {
 		maybe_string fast_dev;
 	};
 
+	class copy_visitor : public mapping_visitor {
+	public:
+		copy_visitor(copier &c, bool only_dirty)
+			: copier_(c),
+			  block_size_(c.get_block_size()),
+			  only_dirty_(only_dirty) {
+		}
+
+		virtual void visit(block_address cblock, mapping const &m) {
+			if (!(m.flags_ & M_VALID))
+				return;
+
+			if (only_dirty_ && !(m.flags_ & M_DIRTY))
+				return;
+
+			auto sectors_copied = copier_.copy(cblock, m.oblock_);
+
+			stats_.blocks_issued++;
+			if (sectors_copied < block_size_) {
+				stats_.blocks_failed++;
+				stats_.sectors_failed += block_size_ - sectors_copied;
+			}
+		}
+
+		struct copy_stats {
+			copy_stats()
+				: blocks_issued(0),
+				  blocks_failed(0),
+				  sectors_failed(0) {
+			}
+
+			block_address blocks_issued;
+			block_address blocks_failed;
+			block_address sectors_failed;
+		};
+
+		copy_stats const &get_stats() const {
+			return stats_;
+		}
+
+	private:
+		copier &copier_;
+		unsigned block_size_;
+		bool only_dirty_;
+		copy_stats stats_;
+	};
+
+	using namespace mapping_array_damage;
+
+	class ignore_damage_visitor : public damage_visitor {
+	public:
+		ignore_damage_visitor()
+			: corruption_(false) {
+		}
+
+		void visit(missing_mappings const &d) {
+			cerr << "missing mappings (" << d.keys_.begin_ << ", " << d.keys_.end_ << "]\n";
+			corruption_ = true;
+		}
+
+		void visit(invalid_mapping const &d) {
+			cerr << "invalid mapping cblock = " << d.cblock_ << ", oblock = " << d.m_.oblock_ << "\n";
+			corruption_ = true;
+		}
+
+		bool was_corruption() const {
+			return corruption_;
+		}
+
+	private:
+		bool corruption_;
+	};
+
+	bool clean_shutdown(metadata const &md) {
+		return md.sb_.flags.get_flag(superblock_flags::CLEAN_SHUTDOWN);
+	}
+
+	int writeback_(flags const &f) {
+		block_manager<>::ptr bm = open_bm(*f.metadata_dev, block_manager<>::READ_ONLY);
+		metadata md(bm, metadata::OPEN);
+
+		copier c(*f.fast_dev, *f.origin_dev, md.sb_.data_block_size);
+		copy_visitor cv(c, clean_shutdown(md));
+		ignore_damage_visitor dv;
+		walk_mapping_array(*md.mappings_, cv, dv);
+
+		auto stats = cv.get_stats();
+		cout << stats.blocks_issued << " copies issued\n"
+		     << stats.blocks_failed << " copies failed\n";
+
+		if (stats.blocks_failed)
+			cout << stats.sectors_failed << " sectors were not copied\n";
+
+		if (dv.was_corruption())
+			cout << "Metadata corruption was found, some data may not have been copied.\n";
+
+		return (stats.blocks_failed || dv.was_corruption()) ? 1 : 0;
+	}
+
 	int writeback(flags const &f) {
-		return 1;
+		int r;
+
+		try {
+			r = writeback_(f);
+
+		} catch (std::exception &e) {
+			cerr << e.what() << endl;
+			return 1;
+		}
+
+		return r;
 	}
 }
 
@@ -118,5 +230,3 @@ cache_writeback_cmd::run(int argc, char **argv)
 }
 
 //----------------------------------------------------------------
-
-#endif