diff --git a/tsdb/engine.go b/tsdb/engine.go
index b4fe3cfa8a..73cf94ff9f 100644
--- a/tsdb/engine.go
+++ b/tsdb/engine.go
@@ -49,6 +49,7 @@ type Engine interface {
 
 	// Statistics will return statistics relevant to this engine.
 	Statistics(tags map[string]string) []models.Statistic
+	LastModified() time.Time
 
 	io.WriterTo
 }
diff --git a/tsdb/engine/tsm1/engine.go b/tsdb/engine/tsm1/engine.go
index 9f40733338..e0fc32f809 100644
--- a/tsdb/engine/tsm1/engine.go
+++ b/tsdb/engine/tsm1/engine.go
@@ -827,6 +827,18 @@ func (e *Engine) SeriesCount() (n int, err error) {
 	return e.index.SeriesN(), nil
 }
 
+// LastModified returns the time when this shard was last modified
+func (e *Engine) LastModified() time.Time {
+	walTime := e.WAL.LastWriteTime()
+	fsTime := e.FileStore.LastModified()
+
+	if walTime.After(fsTime) {
+		return walTime
+	}
+
+	return fsTime
+}
+
 func (e *Engine) WriteTo(w io.Writer) (n int64, err error) { panic("not implemented") }
 
 // WriteSnapshot will snapshot the cache and write a new TSM file with its contents, releasing the snapshot when done.
diff --git a/tsdb/engine/tsm1/engine_test.go b/tsdb/engine/tsm1/engine_test.go
index ed688a7fb8..e26355fb40 100644
--- a/tsdb/engine/tsm1/engine_test.go
+++ b/tsdb/engine/tsm1/engine_test.go
@@ -609,6 +609,63 @@ func TestEngine_DeleteSeries(t *testing.T) {
 
 }
 
+func TestEngine_LastModified(t *testing.T) {
+	// Generate temporary file.
+	dir, _ := ioutil.TempDir("", "tsm")
+	walPath := filepath.Join(dir, "wal")
+	os.MkdirAll(walPath, 0777)
+	defer os.RemoveAll(dir)
+
+	// Create a few points.
+	p1 := MustParsePointString("cpu,host=A value=1.1 1000000000")
+	p2 := MustParsePointString("cpu,host=B value=1.2 2000000000")
+	p3 := MustParsePointString("cpu,host=A sum=1.3 3000000000")
+
+	// Write those points to the engine.
+	e := tsm1.NewEngine(1, dir, walPath, tsdb.NewEngineOptions()).(*tsm1.Engine)
+
+	// mock the planner so compactions don't run during the test
+	e.CompactionPlan = &mockPlanner{}
+
+	if lm := e.LastModified(); !lm.IsZero() {
+		t.Fatalf("expected zero time, got %v", lm.UTC())
+	}
+
+	e.SetEnabled(false)
+	if err := e.Open(); err != nil {
+		t.Fatalf("failed to open tsm1 engine: %s", err.Error())
+	}
+
+	if err := e.WritePoints([]models.Point{p1, p2, p3}); err != nil {
+		t.Fatalf("failed to write points: %s", err.Error())
+	}
+
+	lm := e.LastModified()
+	if lm.IsZero() {
+		t.Fatalf("expected non-zero time, got %v", lm.UTC())
+	}
+	e.SetEnabled(true)
+
+	if err := e.WriteSnapshot(); err != nil {
+		t.Fatalf("failed to snapshot: %s", err.Error())
+	}
+
+	lm2 := e.LastModified()
+
+	if got, exp := lm.Equal(lm2), false; exp != got {
+		t.Fatalf("expected time change, got %v, exp %v", got, exp)
+	}
+
+	if err := e.DeleteSeries([]string{"cpu,host=A"}); err != nil {
+		t.Fatalf("failed to delete series: %v", err)
+	}
+
+	lm3 := e.LastModified()
+	if got, exp := lm2.Equal(lm3), false; exp != got {
+		t.Fatalf("expected time change, got %v, exp %v", got, exp)
+	}
+}
+
 func BenchmarkEngine_CreateIterator_Count_1K(b *testing.B) {
 	benchmarkEngineCreateIteratorCount(b, 1000)
 }
diff --git a/tsdb/engine/tsm1/file_store.go b/tsdb/engine/tsm1/file_store.go
index fdac2daeaf..d34ba06da0 100644
--- a/tsdb/engine/tsm1/file_store.go
+++ b/tsdb/engine/tsm1/file_store.go
@@ -171,7 +171,7 @@ func NewFileStore(dir string) *FileStore {
 	logger := log.New(os.Stderr, "[filestore] ", log.LstdFlags)
 	fs := &FileStore{
 		dir:          dir,
-		lastModified: time.Now(),
+		lastModified: time.Time{},
 		logger:       logger,
 		traceLogger:  log.New(ioutil.Discard, "[filestore] ", log.LstdFlags),
 		logOutput:    os.Stderr,
@@ -347,7 +347,7 @@ func (f *FileStore) Delete(keys []string) error {
 // DeleteRange removes the values for keys between min and max.
 func (f *FileStore) DeleteRange(keys []string, min, max int64) error {
 	f.mu.Lock()
-	f.lastModified = time.Now()
+	f.lastModified = time.Now().UTC()
 	f.mu.Unlock()
 
 	return f.walkFiles(func(tsm TSMFile) error {
@@ -411,8 +411,12 @@ func (f *FileStore) Open() error {
 		}
 
 		// Accumulate file store size stat
-		if fi, err := file.Stat(); err == nil {
+		fi, err := file.Stat()
+		if err == nil {
 			atomic.AddInt64(&f.stats.DiskBytes, fi.Size())
+			if fi.ModTime().UTC().After(f.lastModified) {
+				f.lastModified = fi.ModTime().UTC()
+			}
 		}
 
 		go func(idx int, file *os.File) {
@@ -515,10 +519,14 @@ func (f *FileStore) Stats() []FileStat {
 }
 
 func (f *FileStore) Replace(oldFiles, newFiles []string) error {
+	if len(oldFiles) == 0 && len(newFiles) == 0 {
+		return nil
+	}
+
 	f.mu.Lock()
 	defer f.mu.Unlock()
 
-	f.lastModified = time.Now()
+	maxTime := f.lastModified
 
 	// Copy the current set of active files while we rename
 	// and load the new files.  We copy the pointers here to minimize
@@ -545,6 +553,13 @@ func (f *FileStore) Replace(oldFiles, newFiles []string) error {
 			return err
 		}
 
+		// Keep track of the new mod time
+		if stat, err := fd.Stat(); err == nil {
+			if stat.ModTime().UTC().After(maxTime) {
+				maxTime = stat.ModTime().UTC()
+			}
+		}
+
 		tsm, err := NewTSMReader(fd)
 		if err != nil {
 			return err
@@ -618,6 +633,15 @@ func (f *FileStore) Replace(oldFiles, newFiles []string) error {
 	// Tell the purger about our in-use files we need to remove
 	f.purger.add(inuse)
 
+	// If times didn't change (which can happen since file mod times are second level),
+	// then add a ns to the time to ensure that lastModified changes since files on disk
+	// actually did change
+	if maxTime.Equal(f.lastModified) {
+		maxTime = maxTime.UTC().Add(1)
+	}
+
+	f.lastModified = maxTime.UTC()
+
 	f.lastFileStats = nil
 	f.files = active
 	sort.Sort(tsmReaders(f.files))
diff --git a/tsdb/engine/tsm1/wal.go b/tsdb/engine/tsm1/wal.go
index 0f8aa0bc7e..6f56fc6942 100644
--- a/tsdb/engine/tsm1/wal.go
+++ b/tsdb/engine/tsm1/wal.go
@@ -212,13 +212,14 @@ func (l *WAL) Open() error {
 		}
 
 		totalOldDiskSize += stat.Size()
+		if stat.ModTime().After(l.lastWriteTime) {
+			l.lastWriteTime = stat.ModTime().UTC()
+		}
 	}
 	atomic.StoreInt64(&l.stats.OldBytes, totalOldDiskSize)
 
 	l.closing = make(chan struct{})
 
-	l.lastWriteTime = time.Now()
-
 	return nil
 }
 
@@ -462,6 +463,10 @@ func (l *WAL) newSegmentFile() error {
 	}
 	l.currentSegmentWriter = NewWALSegmentWriter(fd)
 
+	if stat, err := fd.Stat(); err == nil {
+		l.lastWriteTime = stat.ModTime()
+	}
+
 	// Reset the current segment size stat
 	atomic.StoreInt64(&l.stats.CurrentBytes, 0)
 
diff --git a/tsdb/shard.go b/tsdb/shard.go
index f0b5a09e89..39b0f7031b 100644
--- a/tsdb/shard.go
+++ b/tsdb/shard.go
@@ -335,6 +335,14 @@ func (s *Shard) ready() error {
 	return err
 }
 
+// LastModified returns the time when this shard was last modified
+func (s *Shard) LastModified() time.Time {
+	if err := s.ready(); err != nil {
+		return time.Time{}
+	}
+	return s.engine.LastModified()
+}
+
 // DiskSize returns the size on disk of this shard
 func (s *Shard) DiskSize() (int64, error) {
 	var size int64