diff --git a/autobatch/autobatch.go b/autobatch/autobatch.go
index 4eb089bf5f4a806b0c613c65b3586861d3c18c45..0f86764525bd824f4f433663070bbec35044e850 100644
--- a/autobatch/autobatch.go
+++ b/autobatch/autobatch.go
@@ -64,6 +64,35 @@ func (d *Datastore) Put(k ds.Key, val []byte) error {
 	return nil
 }
 
+// Sync flushes all operations on keys at or under the prefix
+// from the current batch to the underlying datastore
+func (d *Datastore) Sync(prefix ds.Key) error {
+	b, err := d.child.Batch()
+	if err != nil {
+		return err
+	}
+
+	for k, o := range d.buffer {
+		if !(k.Equal(prefix) || k.IsDescendantOf(prefix)) {
+			continue
+		}
+
+		var err error
+		if o.delete {
+			err = b.Delete(k)
+		} else {
+			err = b.Put(k, o.value)
+		}
+		if err != nil {
+			return err
+		}
+
+		delete(d.buffer, k)
+	}
+
+	return b.Commit()
+}
+
 // Flush flushes the current batch to the underlying datastore.
 func (d *Datastore) Flush() error {
 	b, err := d.child.Batch()
diff --git a/autobatch/autobatch_test.go b/autobatch/autobatch_test.go
index 0dcf2a0c5d6bf77daadd4546159b637a4f108571..bd6fb30075cd662111d1481ad72f772e42a02f27 100644
--- a/autobatch/autobatch_test.go
+++ b/autobatch/autobatch_test.go
@@ -103,3 +103,149 @@ func TestFlushing(t *testing.T) {
 		t.Fatal("wrong value")
 	}
 }
+
+func TestSync(t *testing.T) {
+	child := ds.NewMapDatastore()
+	d := NewAutoBatching(child, 100)
+
+	put := func(key ds.Key) {
+		if err := d.Put(key, []byte(key.String())); err != nil {
+			t.Fatal(err)
+		}
+	}
+	del := func(key ds.Key) {
+		if err := d.Delete(key); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	get := func(d ds.Datastore, key ds.Key) {
+		val, err := d.Get(key)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !bytes.Equal(val, []byte(key.String())) {
+			t.Fatal("wrong value")
+		}
+	}
+	invalidGet := func(d ds.Datastore, key ds.Key) {
+		if _, err := d.Get(key); err != ds.ErrNotFound {
+			t.Fatal("should not have found value")
+		}
+	}
+
+	// Test if Syncing Puts works
+	internalSyncTest(t, d, child, put, del, get, invalidGet)
+
+	// Test if Syncing Deletes works
+	internalSyncTest(t, d, child, del, put, invalidGet, get)
+}
+
+// This function can be used to test Sync Puts and Deletes
+// For clarity comments are written as if op = Put and undoOp = Delete
+func internalSyncTest(t *testing.T, d, child ds.Datastore, op, undoOp func(ds.Key),
+	checkOp, checkUndoOp func(ds.Datastore, ds.Key)) {
+	var keys []ds.Key
+	keymap := make(map[ds.Key]int)
+	for i := 0; i < 4; i++ {
+		k := ds.NewKey(fmt.Sprintf("%d", i))
+		keymap[k] = len(keys)
+		keys = append(keys, k)
+		for j := 0; j < 2; j++ {
+			k := ds.NewKey(fmt.Sprintf("%d/%d", i, j))
+			keymap[k] = len(keys)
+			keys = append(keys, k)
+			for k := 0; k < 2; k++ {
+				k := ds.NewKey(fmt.Sprintf("%d/%d/%d", i, j, k))
+				keymap[k] = len(keys)
+				keys = append(keys, k)
+			}
+		}
+	}
+
+	for _, k := range keys {
+		op(k)
+	}
+
+	// Get works normally.
+	for _, k := range keys {
+		checkOp(d, k)
+	}
+
+	// Put not flushed
+	checkUndoOp(child, ds.NewKey("0"))
+
+	// Delete works.
+	deletedKey := ds.NewKey("2/1/1")
+	undoOp(deletedKey)
+	checkUndoOp(d, deletedKey)
+
+	// Put still not flushed
+	checkUndoOp(child, ds.NewKey("0"))
+
+	// Sync the tree "0/*/*"
+	if err := d.Sync(ds.NewKey("0")); err != nil {
+		t.Fatal(err)
+	}
+
+	// Try to get keys "0/*/*" from the child datastore
+	checkKeyRange(t, keymap, keys, d, [][]string{{"0", "0/1/1"}}, checkOp)
+
+	// Verify no other keys were synchronized
+	checkKeyRange(t, keymap, keys, child, [][]string{{"1", "3/1/1"}}, checkUndoOp)
+
+	// Sync the tree "1/1/*"
+	if err := d.Sync(ds.NewKey("1/1")); err != nil {
+		t.Fatal(err)
+	}
+
+	// Try to get keys "0/*/*" and "1/1/*" from the child datastore
+	checkKeyRange(t, keymap, keys, d, [][]string{{"0", "0/1/1"}, {"1/1", "1/1/1"}}, checkOp)
+
+	// Verify no other keys were synchronized
+	checkKeyRange(t, keymap, keys, child, [][]string{{"1", "1/0/1"}, {"2", "3/1/1"}}, checkUndoOp)
+
+	// Sync the tree "3/1/1"
+	if err := d.Sync(ds.NewKey("3/1/1")); err != nil {
+		t.Fatal(err)
+	}
+
+	// Try to get keys "0/*/*", "1/1/*", "3/1/1" from the child datastore
+	checkKeyRange(t, keymap, keys, d, [][]string{{"0", "0/1/1"}, {"1/1", "1/1/1"}, {"3/1/1", "3/1/1"}}, checkOp)
+
+	// Verify no other keys were synchronized
+	checkKeyRange(t, keymap, keys, child, [][]string{{"1", "1/0/1"}, {"2", "3/1/0"}}, checkUndoOp)
+
+	if err := d.Sync(ds.Key{}); err != nil {
+		t.Fatal(err)
+	}
+
+	// Never flushed the deleted key.
+	checkUndoOp(child, deletedKey)
+
+	// Try to get all keys except the deleted key from the child datastore
+	checkKeyRange(t, keymap, keys, d, [][]string{{"0", "2/1/0"}, {"3", "3/1/1"}}, checkOp)
+
+	// Add the deleted key into the datastore
+	op(deletedKey)
+
+	// Sync it
+	if err := d.Sync(deletedKey); err != nil {
+		t.Fatal(err)
+	}
+
+	// Check it
+	checkOp(d, deletedKey)
+}
+
+func checkKeyRange(t *testing.T, keymap map[ds.Key]int, keys []ds.Key,
+	d ds.Datastore, validKeyRanges [][]string, checkFn func(ds.Datastore, ds.Key)) {
+	t.Helper()
+	for _, validKeyBoundaries := range validKeyRanges {
+		start, end := keymap[ds.NewKey(validKeyBoundaries[0])], keymap[ds.NewKey(validKeyBoundaries[1])]
+		for _, k := range keys[start:end] {
+			checkFn(d, k)
+		}
+	}
+}
diff --git a/basic_ds.go b/basic_ds.go
index 98476767f1ddace487f097811f0b02162a0c1c3b..46567cc0246af229a4da35ec7a1d5c283c93ba87 100644
--- a/basic_ds.go
+++ b/basic_ds.go
@@ -28,6 +28,11 @@ func (d *MapDatastore) Put(key Key, value []byte) (err error) {
 	return nil
 }
 
+// Sync implements Datastore.Sync
+func (d *MapDatastore) Sync(prefix Key) error {
+	return nil
+}
+
 // Get implements Datastore.Get
 func (d *MapDatastore) Get(key Key) (value []byte, err error) {
 	val, found := d.values[key]
@@ -95,6 +100,11 @@ func (d *NullDatastore) Put(key Key, value []byte) (err error) {
 	return nil
 }
 
+// Sync implements Datastore.Sync
+func (d *NullDatastore) Sync(prefix Key) error {
+	return nil
+}
+
 // Get implements Datastore.Get
 func (d *NullDatastore) Get(key Key) (value []byte, err error) {
 	return nil, ErrNotFound
diff --git a/datastore.go b/datastore.go
index 7715c47ebd32fff18705f7a75686638793e67745..04ca726c4ab346bf3af0210a5e0cbc8326c17839 100644
--- a/datastore.go
+++ b/datastore.go
@@ -34,6 +34,13 @@ should be checked by callers.
 type Datastore interface {
 	Read
 	Write
+	// Sync guarantees that any Put or Delete calls under prefix that returned
+	// before Sync(prefix) was called will be observed after Sync(prefix)
+	// returns, even if the program crashes. If Put/Delete operations already
+	// satisfy these requirements then Sync may be a no-op.
+	//
+	// If the prefix fails to Sync this method returns an error.
+	Sync(prefix Key) error
 	io.Closer
 }
 
diff --git a/delayed/delayed.go b/delayed/delayed.go
index d34909fe8d694638eccb998754dfa9a843315d7c..f634c947c7be7e8ebcc33f619f41ebc6f861babd 100644
--- a/delayed/delayed.go
+++ b/delayed/delayed.go
@@ -30,6 +30,12 @@ func (dds *Delayed) Put(key ds.Key, value []byte) (err error) {
 	return dds.ds.Put(key, value)
 }
 
+// Sync implements Datastore.Sync
+func (dds *Delayed) Sync(prefix ds.Key) error {
+	dds.delay.Wait()
+	return dds.ds.Sync(prefix)
+}
+
 // Get implements the ds.Datastore interface.
 func (dds *Delayed) Get(key ds.Key) (value []byte, err error) {
 	dds.delay.Wait()
diff --git a/examples/fs.go b/examples/fs.go
index 87369e811384a3d70dc3b38290d2cf18853b8fd6..a5fda62be3cfb098756099b96ab3d025a80c3008 100644
--- a/examples/fs.go
+++ b/examples/fs.go
@@ -63,6 +63,12 @@ func (d *Datastore) Put(key ds.Key, value []byte) (err error) {
 	return ioutil.WriteFile(fn, value, 0666)
 }
 
+// Sync would ensure that any previous Puts under the prefix are written to disk.
+// However, they already are.
+func (d *Datastore) Sync(prefix ds.Key) error {
+	return nil
+}
+
 // Get returns the value for given key
 func (d *Datastore) Get(key ds.Key) (value []byte, err error) {
 	fn := d.KeyFilename(key)
@@ -103,8 +109,9 @@ func (d *Datastore) Query(q query.Query) (query.Results, error) {
 
 	walkFn := func(path string, info os.FileInfo, err error) error {
 		// remove ds path prefix
-		if strings.HasPrefix(path, d.path) {
-			path = path[len(d.path):]
+		relPath, err := filepath.Rel(d.path, path)
+		if err == nil {
+			path = filepath.ToSlash(relPath)
 		}
 
 		if !info.IsDir() {
@@ -167,7 +174,7 @@ func (d *Datastore) DiskUsage() (uint64, error) {
 			log.Println(err)
 			return err
 		}
-		if f != nil {
+		if f != nil && f.Mode().IsRegular() {
 			du += uint64(f.Size())
 		}
 		return nil
diff --git a/examples/fs_test.go b/examples/fs_test.go
index 19be7a05ee455b83c98d709d24b8ee9f9e54a4a1..5ee54d39645623417bb455ce3422c13ac564289c 100644
--- a/examples/fs_test.go
+++ b/examples/fs_test.go
@@ -96,13 +96,16 @@ func (ks *DSSuite) TestDiskUsage(c *C) {
 		"foo/bar/baz/barb",
 	})
 
+	totalBytes := 0
 	for _, k := range keys {
-		err := ks.ds.Put(k, []byte(k.String()))
+		value := []byte(k.String())
+		totalBytes += len(value)
+		err := ks.ds.Put(k, value)
 		c.Check(err, Equals, nil)
 	}
 
 	if ps, ok := ks.ds.(ds.PersistentDatastore); ok {
-		if s, err := ps.DiskUsage(); s <= 100 || err != nil {
+		if s, err := ps.DiskUsage(); s != uint64(totalBytes) || err != nil {
 			c.Error("unexpected size is: ", s)
 		}
 	} else {
diff --git a/failstore/failstore.go b/failstore/failstore.go
index 1408a3ef9a0e961da0f70359d2555b0136be44ba..f790f96e74af99c07e5ea5f4e71cda101f7802db 100644
--- a/failstore/failstore.go
+++ b/failstore/failstore.go
@@ -36,6 +36,16 @@ func (d *Failstore) Put(k ds.Key, val []byte) error {
 	return d.child.Put(k, val)
 }
 
+// Sync implements Datastore.Sync
+func (d *Failstore) Sync(prefix ds.Key) error {
+	err := d.errfunc("sync")
+	if err != nil {
+		return err
+	}
+
+	return d.child.Sync(prefix)
+}
+
 // Get retrieves a value from the datastore.
 func (d *Failstore) Get(k ds.Key) ([]byte, error) {
 	err := d.errfunc("get")
diff --git a/keytransform/keytransform.go b/keytransform/keytransform.go
index ae0297307f014dba0d759fb0879a2a9fd08d98c5..cd03487ca06aafeb95e590fe953eeff8e6dccfdf 100644
--- a/keytransform/keytransform.go
+++ b/keytransform/keytransform.go
@@ -37,6 +37,11 @@ func (d *Datastore) Put(key ds.Key, value []byte) (err error) {
 	return d.child.Put(d.ConvertKey(key), value)
 }
 
+// Sync implements Datastore.Sync
+func (d *Datastore) Sync(prefix ds.Key) error {
+	return d.child.Sync(d.ConvertKey(prefix))
+}
+
 // Get returns the value for given key, transforming the key first.
 func (d *Datastore) Get(key ds.Key) (value []byte, err error) {
 	return d.child.Get(d.ConvertKey(key))
diff --git a/mount/mount.go b/mount/mount.go
index c092c262a13a16b31886b39b361402b744635f97..d2556b2e0786f405f3d87e1baecf798436dbd7c6 100644
--- a/mount/mount.go
+++ b/mount/mount.go
@@ -189,6 +189,24 @@ func (d *Datastore) Put(key ds.Key, value []byte) error {
 	return cds.Put(k, value)
 }
 
+// Sync implements Datastore.Sync
+func (d *Datastore) Sync(prefix ds.Key) error {
+	// Sync all mount points below the prefix
+	// Sync the mount point right at (or above) the prefix
+	dstores, mountPts, rest := d.lookupAll(prefix)
+	for i, suffix := range rest {
+		if err := dstores[i].Sync(suffix); err != nil {
+			return err
+		}
+
+		if mountPts[i].Equal(prefix) || suffix.String() != "/" {
+			return nil
+		}
+	}
+
+	return nil
+}
+
 func (d *Datastore) Get(key ds.Key) (value []byte, err error) {
 	cds, _, k := d.lookup(key)
 	if cds == nil {
diff --git a/mount/mount_test.go b/mount/mount_test.go
index 36135363d3578de25b03d2426ffe62ac49f6e2aa..497ba2db951e8df6c594a4822ee22d4b8517c792 100644
--- a/mount/mount_test.go
+++ b/mount/mount_test.go
@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	datastore "github.com/ipfs/go-datastore"
+	autobatch "github.com/ipfs/go-datastore/autobatch"
 	mount "github.com/ipfs/go-datastore/mount"
 	query "github.com/ipfs/go-datastore/query"
 	sync "github.com/ipfs/go-datastore/sync"
@@ -641,6 +642,70 @@ func TestLookupPrio(t *testing.T) {
 	}
 }
 
+func TestNestedMountSync(t *testing.T) {
+	internalDSRoot := datastore.NewMapDatastore()
+	internalDSFoo := datastore.NewMapDatastore()
+	internalDSFooBar := datastore.NewMapDatastore()
+
+	m := mount.New([]mount.Mount{
+		{Prefix: datastore.NewKey("/foo"), Datastore: autobatch.NewAutoBatching(internalDSFoo, 10)},
+		{Prefix: datastore.NewKey("/foo/bar"), Datastore: autobatch.NewAutoBatching(internalDSFooBar, 10)},
+		{Prefix: datastore.NewKey("/"), Datastore: autobatch.NewAutoBatching(internalDSRoot, 10)},
+	})
+
+	// Testing scenarios
+	// 1) Make sure child(ren) sync
+	// 2) Make sure parent syncs
+	// 3) Make sure parent only syncs the relevant subtree (instead of fully syncing)
+
+	addToDS := func(str string) {
+		t.Helper()
+		if err := m.Put(datastore.NewKey(str), []byte(str)); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	checkVal := func(d datastore.Datastore, str string, expectFound bool) {
+		t.Helper()
+		res, err := d.Has(datastore.NewKey(str))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if res != expectFound {
+			if expectFound {
+				t.Fatal("datastore is missing key")
+			}
+			t.Fatal("datastore has key it should not have")
+		}
+	}
+
+	// Add /foo/bar/0, Add /foo/bar/0/1, Add /foo/baz, Add /beep/bop, Sync /foo: all added except last - checks 1 and 2
+	addToDS("/foo/bar/0")
+	addToDS("/foo/bar/1")
+	addToDS("/foo/baz")
+	addToDS("/beep/bop")
+
+	if err := m.Sync(datastore.NewKey("/foo")); err != nil {
+		t.Fatal(err)
+	}
+
+	checkVal(internalDSFooBar, "/0", true)
+	checkVal(internalDSFooBar, "/1", true)
+	checkVal(internalDSFoo, "/baz", true)
+	checkVal(internalDSRoot, "/beep/bop", false)
+
+	// Add /fwop Add /bloop Sync /fwop, both added - checks 3
+	addToDS("/fwop")
+	addToDS("/bloop")
+
+	if err := m.Sync(datastore.NewKey("/fwop")); err != nil {
+		t.Fatal(err)
+	}
+
+	checkVal(internalDSRoot, "/fwop", true)
+	checkVal(internalDSRoot, "/bloop", false)
+}
+
 type errQueryDS struct {
 	datastore.NullDatastore
 }
diff --git a/retrystore/retrystore.go b/retrystore/retrystore.go
index 02e44ab3d5a0cd4c468a707638445c67e3ac0aba..d4527581617ea37e354c5606f3bc083fedcd8ca3 100644
--- a/retrystore/retrystore.go
+++ b/retrystore/retrystore.go
@@ -73,6 +73,13 @@ func (d *Datastore) Put(k ds.Key, val []byte) error {
 	})
 }
 
+// Sync implements Datastore.Sync
+func (d *Datastore) Sync(prefix ds.Key) error {
+	return d.runOp(func() error {
+		return d.Batching.Sync(prefix)
+	})
+}
+
 // Has checks if a key is stored.
 func (d *Datastore) Has(k ds.Key) (bool, error) {
 	var has bool
diff --git a/sync/sync.go b/sync/sync.go
index 5a4bb0e774a78014c6119aa4901610734a8b1ed9..3eb7290ee6b753f7427eb929a6bb5cc24949e2d5 100644
--- a/sync/sync.go
+++ b/sync/sync.go
@@ -33,6 +33,13 @@ func (d *MutexDatastore) Put(key ds.Key, value []byte) (err error) {
 	return d.child.Put(key, value)
 }
 
+// Sync implements Datastore.Sync
+func (d *MutexDatastore) Sync(prefix ds.Key) error {
+	d.Lock()
+	defer d.Unlock()
+	return d.child.Sync(prefix)
+}
+
 // Get implements Datastore.Get
 func (d *MutexDatastore) Get(key ds.Key) (value []byte, err error) {
 	d.RLock()
diff --git a/test/basic_tests.go b/test/basic_tests.go
index b1c73de55f99a4828c93e01bdd7ab5873b62cea0..0506ee531c3d6d4931ce5c66aac3857d9aad3e66 100644
--- a/test/basic_tests.go
+++ b/test/basic_tests.go
@@ -176,6 +176,36 @@ func SubtestManyKeysAndQuery(t *testing.T, ds dstore.Datastore) {
 	subtestQuery(t, ds, dsq.Query{KeysOnly: true}, 100)
 }
 
+func SubtestBasicSync(t *testing.T, ds dstore.Datastore) {
+	if err := ds.Sync(dstore.NewKey("foo")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ds.Put(dstore.NewKey("/foo"), []byte("foo")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ds.Sync(dstore.NewKey("/foo")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ds.Put(dstore.NewKey("/foo/bar"), []byte("bar")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ds.Sync(dstore.NewKey("/foo")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ds.Sync(dstore.NewKey("/foo/bar")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ds.Sync(dstore.NewKey("")); err != nil {
+		t.Fatal(err)
+	}
+}
+
 // need a custom test filter to test the "fallback" filter case for unknown
 // filters.
 type testFilter struct{}
diff --git a/test/suite.go b/test/suite.go
index 3d1740115f474814da8aea023fb2775a9282edbb..afebd1ca813e5cb46c5fd2439e08d0d2f8eef932 100644
--- a/test/suite.go
+++ b/test/suite.go
@@ -19,6 +19,7 @@ var BasicSubtests = []func(t *testing.T, ds dstore.Datastore){
 	SubtestFilter,
 	SubtestManyKeysAndQuery,
 	SubtestReturnSizes,
+	SubtestBasicSync,
 }
 
 // BatchSubtests is a list of all basic batching datastore tests.