diff --git a/backend/id_set.go b/backend/id_set.go
deleted file mode 100644
index 253147605..000000000
--- a/backend/id_set.go
+++ /dev/null
@@ -1,75 +0,0 @@
-package backend
-
-import (
-	"errors"
-	"sort"
-	"sync"
-)
-
-type IDSet struct {
-	list IDs
-	m    sync.Mutex
-}
-
-func NewIDSet() *IDSet {
-	return &IDSet{
-		list: make(IDs, 0),
-	}
-}
-
-func (s *IDSet) find(id ID) (int, error) {
-	pos := sort.Search(len(s.list), func(i int) bool {
-		return id.Compare(s.list[i]) >= 0
-	})
-
-	if pos < len(s.list) {
-		candID := s.list[pos]
-		if id.Compare(candID) == 0 {
-			return pos, nil
-		}
-	}
-
-	return pos, errors.New("ID not found")
-}
-
-func (s *IDSet) insert(id ID) {
-	pos, err := s.find(id)
-	if err == nil {
-		// already present
-		return
-	}
-
-	// insert blob
-	// https://code.google.com/p/go-wiki/wiki/SliceTricks
-	s.list = append(s.list, ID{})
-	copy(s.list[pos+1:], s.list[pos:])
-	s.list[pos] = id
-
-	return
-}
-
-func (s *IDSet) Insert(id ID) {
-	s.m.Lock()
-	defer s.m.Unlock()
-
-	s.insert(id)
-}
-
-func (s *IDSet) Find(id ID) error {
-	s.m.Lock()
-	defer s.m.Unlock()
-
-	_, err := s.find(id)
-	if err != nil {
-		return err
-	}
-
-	return nil
-}
-
-func (s *IDSet) Len() int {
-	s.m.Lock()
-	defer s.m.Unlock()
-
-	return len(s.list)
-}
diff --git a/backend/id_set_test.go b/backend/id_set_test.go
deleted file mode 100644
index 4b8139a36..000000000
--- a/backend/id_set_test.go
+++ /dev/null
@@ -1,41 +0,0 @@
-package backend_test
-
-import (
-	"crypto/rand"
-	"io"
-	"testing"
-
-	"github.com/restic/restic/backend"
-	. "github.com/restic/restic/test"
-)
-
-func randomID() []byte {
-	buf := make([]byte, backend.IDSize)
-	_, err := io.ReadFull(rand.Reader, buf)
-	if err != nil {
-		panic(err)
-	}
-	return buf
-}
-
-func TestSet(t *testing.T) {
-	s := backend.NewIDSet()
-
-	testID := randomID()
-	err := s.Find(testID)
-	Assert(t, err != nil, "found test ID in IDSet before insertion")
-
-	for i := 0; i < 238; i++ {
-		s.Insert(randomID())
-	}
-
-	s.Insert(testID)
-	OK(t, s.Find(testID))
-
-	for i := 0; i < 80; i++ {
-		s.Insert(randomID())
-	}
-
-	s.Insert(testID)
-	OK(t, s.Find(testID))
-}