diff --git a/thin-provisioning/device_checker.cc b/thin-provisioning/device_checker.cc
index dcca01b..071a2ca 100644
--- a/thin-provisioning/device_checker.cc
+++ b/thin-provisioning/device_checker.cc
@@ -1,19 +1,103 @@
 #include "thin-provisioning/device_checker.h"
 
+#include "persistent-data/data-structures/btree_checker.h"
+#include "persistent-data/transaction_manager.h"
+#include "persistent-data/space-maps/core.h"
+#include "thin-provisioning/metadata.h"
+#include "thin-provisioning/metadata_disk_structures.h"
+
+using namespace persistent_data;
 using namespace thin_provisioning;
 
 //----------------------------------------------------------------
 
-device_checker::device_checker(block_manager::ptr bm)
-	: checker(bm)
+namespace {
+	// FIXME: duplication with metadata.cc
+	transaction_manager::ptr
+	open_tm(block_manager<>::ptr bm) {
+		space_map::ptr sm(new core_map(bm->get_nr_blocks()));
+		sm->inc(SUPERBLOCK_LOCATION);
+		transaction_manager::ptr tm(new transaction_manager(bm, sm));
+		return tm;
+	}
+
+
+	class device_visitor : public btree<1, device_details_traits>::visitor {
+	public:
+		typedef boost::shared_ptr<device_visitor> ptr;
+		typedef btree_checker<1, device_details_traits> checker;
+
+		device_visitor(block_counter &counter)
+			: checker_(counter) {
+		}
+
+		bool visit_internal(unsigned level,
+				    bool sub_root,
+				    optional<uint64_t> key,
+				    btree_detail::node_ref<uint64_traits> const &n) {
+			return checker_.visit_internal(level, sub_root, key, n);
+		}
+
+		bool visit_internal_leaf(unsigned level,
+					 bool sub_root,
+					 optional<uint64_t> key,
+					 btree_detail::node_ref<uint64_traits> const &n) {
+			return checker_.visit_internal_leaf(level, sub_root, key, n);
+		}
+
+		bool visit_leaf(unsigned level,
+				bool sub_root,
+				optional<uint64_t> key,
+				btree_detail::node_ref<device_details_traits> const &n) {
+
+			if (!checker_.visit_leaf(level, sub_root, key, n))
+				return false;
+
+			for (unsigned i = 0; i < n.get_nr_entries(); i++)
+				devices_.insert(n.key_at(i));
+
+			return true;
+		}
+
+		set<uint64_t> const &get_devices() const {
+			return devices_;
+		}
+
+	private:
+		checker checker_;
+		set<uint64_t> devices_;
+	};
+}
+
+//----------------------------------------------------------------
+
+device_checker::device_checker(block_manager::ptr bm,
+			       block_address root)
+	: checker(bm),
+	  root_(root)
 {
 }
 
 damage_list_ptr
 device_checker::check()
 {
-	// FIXME: finish.
-	return damage_list_ptr(new damage_list);
+	block_counter counter;
+	device_visitor::ptr v(new device_visitor(counter));
+	transaction_manager::ptr tm(open_tm(bm_));
+	detail_tree::ptr details(new detail_tree(tm, root_,
+						 device_details_traits::ref_counter()));
+	damage_list_ptr damage(new damage_list);
+
+	try {
+		details->visit(v);
+
+	} catch (std::exception const &e) {
+
+		metadata_damage::ptr d(new missing_device_details(range64()));
+		damage->push_back(d);
+	}
+
+	return damage;
 }
 
 //----------------------------------------------------------------
diff --git a/thin-provisioning/device_checker.h b/thin-provisioning/device_checker.h
index ff4d561..b2b67d0 100644
--- a/thin-provisioning/device_checker.h
+++ b/thin-provisioning/device_checker.h
@@ -8,8 +8,11 @@
 namespace thin_provisioning {
 	class device_checker : public checker {
 	public:
-		device_checker(block_manager::ptr bm);
+		device_checker(block_manager::ptr bm, block_address btree_root);
 		damage_list_ptr check();
+
+	private:
+		block_address root_;
 	};
 }
 
diff --git a/thin-provisioning/metadata_checker.cc b/thin-provisioning/metadata_checker.cc
index 5276a0b..c4572d4 100644
--- a/thin-provisioning/metadata_checker.cc
+++ b/thin-provisioning/metadata_checker.cc
@@ -48,10 +48,8 @@ super_block_corruption::visit(metadata_damage_visitor &visitor) const
 
 //--------------------------------
 
-missing_device_details::missing_device_details(uint64_t missing_begin,
-					       uint64_t missing_end)
-	: missing_begin_(missing_begin),
-	  missing_end_(missing_end)
+missing_device_details::missing_device_details(range64 missing)
+	: missing_(missing)
 {
 }
 
@@ -63,10 +61,8 @@ missing_device_details::visit(metadata_damage_visitor &visitor) const
 
 //--------------------------------
 
-missing_devices::missing_devices(uint64_t missing_begin,
-				 uint64_t missing_end)
-	: missing_begin_(missing_begin),
-	  missing_end_(missing_end)
+missing_devices::missing_devices(range64 missing)
+	: missing_(missing)
 {
 }
 
@@ -78,12 +74,9 @@ missing_devices::visit(metadata_damage_visitor &visitor) const
 
 //--------------------------------
 
-missing_mappings::missing_mappings(uint64_t dev,
-				   uint64_t missing_begin,
-				   uint64_t missing_end)
+missing_mappings::missing_mappings(uint64_t dev, range64 missing)
 	: dev_(dev),
-	  missing_begin_(missing_begin),
-	  missing_end_(missing_end)
+	  missing_(missing)
 {
 }
 
@@ -129,10 +122,8 @@ bad_data_ref_count::visit(metadata_damage_visitor &visitor) const
 
 //--------------------------------
 
-missing_metadata_ref_counts::missing_metadata_ref_counts(block_address missing_begin,
-							 block_address missing_end)
-	: missing_begin_(missing_begin),
-	  missing_end_(missing_end)
+missing_metadata_ref_counts::missing_metadata_ref_counts(range64 missing)
+	: missing_(missing)
 {
 }
 
@@ -144,10 +135,8 @@ missing_metadata_ref_counts::visit(metadata_damage_visitor &visitor) const
 
 //--------------------------------
 
-missing_data_ref_counts::missing_data_ref_counts(block_address missing_begin,
-						 block_address missing_end)
-	: missing_begin_(missing_begin),
-	  missing_end_(missing_end)
+missing_data_ref_counts::missing_data_ref_counts(range64 missing)
+	: missing_(missing)
 {
 }
 
@@ -236,52 +225,6 @@ namespace {
 		set<uint64_t> devices_;
 	};
 
-	class details_validator : public btree<1, device_details_traits>::visitor {
-	public:
-		typedef boost::shared_ptr<details_validator> ptr;
-		typedef btree_checker<1, device_details_traits> checker;
-
-		details_validator(block_counter &counter)
-			: checker_(counter) {
-		}
-
-		bool visit_internal(unsigned level,
-				    bool sub_root,
-				    optional<uint64_t> key,
-				    btree_detail::node_ref<uint64_traits> const &n) {
-			return checker_.visit_internal(level, sub_root, key, n);
-		}
-
-		bool visit_internal_leaf(unsigned level,
-					 bool sub_root,
-					 optional<uint64_t> key,
-					 btree_detail::node_ref<uint64_traits> const &n) {
-			return checker_.visit_internal_leaf(level, sub_root, key, n);
-		}
-
-		bool visit_leaf(unsigned level,
-				bool sub_root,
-				optional<uint64_t> key,
-				btree_detail::node_ref<device_details_traits> const &n) {
-
-			if (!checker_.visit_leaf(level, sub_root, key, n))
-				return false;
-
-			for (unsigned i = 0; i < n.get_nr_entries(); i++)
-				devices_.insert(n.key_at(i));
-
-			return true;
-		}
-
-		set<uint64_t> const &get_devices() const {
-			return devices_;
-		}
-
-	private:
-		checker checker_;
-		set<uint64_t> devices_;
-	};
-
 	struct check_count : public space_map::iterator {
 		check_count(string const &desc, block_counter const &expected)
 			: bad_(false),
diff --git a/thin-provisioning/metadata_checker.h b/thin-provisioning/metadata_checker.h
index 16f5ebb..d024138 100644
--- a/thin-provisioning/metadata_checker.h
+++ b/thin-provisioning/metadata_checker.h
@@ -23,6 +23,8 @@
 #include "persistent-data/error_set.h"
 #include "persistent-data/space_map.h"
 
+#include "thin-provisioning/range.h"
+
 #include <deque>
 
 //----------------------------------------------------------------
@@ -53,36 +55,28 @@ namespace thin_provisioning {
 		void visit(metadata_damage_visitor &visitor) const;
 	};
 
-	struct missing_device_details : public metadata_damage {
-		missing_device_details(uint64_t missing_begin,
-				       uint64_t missing_end);
+	typedef range<uint64_t> range64;
 
+	struct missing_device_details : public metadata_damage {
+		missing_device_details(range64 missing);
 		virtual void visit(metadata_damage_visitor &visitor) const;
 
-		uint64_t missing_begin_;
-		uint64_t missing_end_;
+		range64 missing_;
 	};
 
 	struct missing_devices : public metadata_damage {
-		missing_devices(uint64_t missing_begin,
-				uint64_t missing_end);
-
+		missing_devices(range64 missing);
 		virtual void visit(metadata_damage_visitor &visitor) const;
 
-		uint64_t missing_begin_;
-		uint64_t missing_end_;
+		range64 missing_;
 	};
 
 	struct missing_mappings : public metadata_damage {
-		missing_mappings(uint64_t dev,
-				 uint64_t missing_begin,
-				 uint64_t missing_end);
-
+		missing_mappings(uint64_t dev, range64 missing);
 		virtual void visit(metadata_damage_visitor &visitor) const;
 
 		uint64_t dev_;
-		uint64_t missing_begin_;
-		uint64_t missing_end_;
+		range64 missing_;
 	};
 
 	struct bad_metadata_ref_count : public metadata_damage {
@@ -110,23 +104,17 @@ namespace thin_provisioning {
 	};
 
 	struct missing_metadata_ref_counts : public metadata_damage {
-		missing_metadata_ref_counts(block_address missing_begin,
-					    block_address missing_end);
-
+		missing_metadata_ref_counts(range64 missing);
 		virtual void visit(metadata_damage_visitor &visitor) const;
 
-		block_address missing_begin_;
-		block_address missing_end_;
+		range64 missing_;
 	};
 
 	struct missing_data_ref_counts : public metadata_damage {
-		missing_data_ref_counts(block_address missing_begin,
-					block_address missing_end);
-
+		missing_data_ref_counts(range64 missing);
 		virtual void visit(metadata_damage_visitor &visitor) const;
 
-		block_address missing_begin_;
-		block_address missing_end_;
+		range64 missing_;
 	};
 
 	class metadata_damage_visitor {
diff --git a/unit-tests/metadata_checker_t.cc b/unit-tests/metadata_checker_t.cc
index 324fee0..348f2bd 100644
--- a/unit-tests/metadata_checker_t.cc
+++ b/unit-tests/metadata_checker_t.cc
@@ -6,6 +6,7 @@
 #include "thin-provisioning/device_checker.h"
 #include "thin-provisioning/restore_emitter.h"
 #include "thin-provisioning/superblock_checker.h"
+#include "thin-provisioning/superblock_validator.h"
 
 #include <unistd.h>
 
@@ -122,24 +123,29 @@ namespace {
 			builder.build();
 		}
 
+		superblock read_superblock() {
+			superblock sb;
+
+			block_manager<>::read_ref r = bm_->read_lock(SUPERBLOCK_LOCATION, superblock_validator());
+			superblock_disk const *sbd = reinterpret_cast<superblock_disk const *>(&r.data());
+			superblock_traits::unpack(*sbd, sb);
+			return sb;
+		}
+
+		void zero_block(block_address b) {
+			::test::zero_block(bm_, b);
+		}
+
 		with_temp_directory dir_;
 		block_manager<>::ptr bm_;
-
 	};
 
 	class SuperBlockCheckerTests : public MetadataCheckerTests {
 	public:
 		void corrupt_superblock() {
-			zero_block(bm_, SUPERBLOCK_LOCATION);
+			zero_block(SUPERBLOCK_LOCATION);
 		}
 	};
-
-	//--------------------------------
-
-	class DevicesCheckerTests : public MetadataCheckerTests {
-	public:
-		
-	};
 }
 
 //----------------------------------------------------------------
@@ -170,9 +176,40 @@ TEST_F(SuperBlockCheckerTests, fails_with_bad_checksum)
 
 //----------------------------------------------------------------
 
-TEST_F(DevicesCheckerTests, create_require_a_block_manager)
+namespace {
+	class DeviceCheckerTests : public MetadataCheckerTests {
+	public:
+		DeviceCheckerTests() {
+		}
+
+		block_address devices_root() {
+			superblock sb = read_superblock();
+			return sb.device_details_root_;
+		}
+
+		device_checker::ptr mk_checker() {
+			return device_checker::ptr(new device_checker(bm_, devices_root()));
+		}
+	};
+}
+
+TEST_F(DeviceCheckerTests, create_require_a_block_manager_and_a_root_block)
 {
-	device_checker dc(bm_);
+	mk_checker();
+}
+
+TEST_F(DeviceCheckerTests, passes_with_valid_metadata_and_zero_devices)
+{
+	damage_list_ptr damage = mk_checker()->check();
+	ASSERT_THAT(damage->size(), Eq(0u));
+}
+
+TEST_F(DeviceCheckerTests, fails_with_corrupt_root)
+{
+	zero_block(devices_root());
+
+	damage_list_ptr damage = mk_checker()->check();
+	ASSERT_THAT(damage->size(), Gt(0u));
 }
 
 //----------------------------------------------------------------