diff --git a/go/storage/cdb_map.go b/go/storage/cdb_map.go
new file mode 100644
index 000000000..ebb49d514
--- /dev/null
+++ b/go/storage/cdb_map.go
@@ -0,0 +1,230 @@
+package storage
+
+import (
+	"code.google.com/p/weed-fs/go/util"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"github.com/tgulacsi/go-cdb"
+	"os"
+	"path/filepath"
+)
+
+// CDB-backed read-only needle map
+type cdbMap struct {
+	c1, c2   *cdb.Cdb
+	fn1, fn2 string
+	mapMetric
+}
+
+const maxCdbRecCount = 100000000
+
+var errReadOnly = errors.New("cannot modify a read-only map")
+
+// opens the cdb file(s) (base.cdb OR base.1.cdb AND base.2.cdb)
+// in case of two files, the metric (at key 'M') must be in base.2.cdb
+func OpenCdbMap(fileName string) (m *cdbMap, err error) {
+	m = new(cdbMap)
+	if m.c1, err = cdb.Open(fileName); err == nil {
+		m.fn1 = fileName
+		err = getMetric(m.c1, &m.mapMetric)
+		return
+	}
+	if os.IsNotExist(err) {
+		bn, ext := nakeFilename(fileName)
+		m.fn1 = bn + ".1" + ext
+		if m.c1, err = cdb.Open(m.fn1); err != nil {
+			return nil, err
+		}
+		m.fn2 = bn + ".2" + ext
+		if m.c2, err = cdb.Open(m.fn2); err != nil {
+			return nil, err
+		}
+		err = getMetric(m.c2, &m.mapMetric)
+		return
+	}
+	return nil, err
+}
+
+func (m *cdbMap) Put(key uint64, offset uint32, size uint32) (int, error) {
+	return -1, errReadOnly
+}
+func (m *cdbMap) Delete(key uint64) error {
+	return errReadOnly
+}
+
+func (m *cdbMap) Close() {
+	if m.c2 != nil {
+		m.c2.Close()
+		m.c2 = nil
+	}
+	if m.c1 != nil {
+		m.c1.Close()
+		m.c1 = nil
+	}
+}
+
+func (m cdbMap) ContentSize() uint64 {
+	return m.FileByteCounter
+}
+func (m cdbMap) DeletedSize() uint64 {
+	return m.DeletionByteCounter
+}
+func (m cdbMap) FileCount() int {
+	return m.FileCounter
+}
+func (m *cdbMap) DeletedCount() int {
+	return m.DeletionCounter
+}
+
+func getMetric(c *cdb.Cdb, m *mapMetric) error {
+	data, err := c.Data([]byte{'M'})
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(data, m)
+}
+
+func (m cdbMap) Get(key uint64) (element *NeedleValue, ok bool) {
+	var (
+		data []byte
+		k    []byte = make([]byte, 8)
+		err  error
+	)
+	util.Uint64toBytes(k, key)
+	if data, err = m.c1.Data(k); err != nil || data == nil {
+		if m.c2 == nil {
+			return nil, false
+		}
+		if data, err = m.c2.Data(k); err != nil || data == nil {
+			return nil, false
+		}
+	}
+	return &NeedleValue{Key: Key(key), Offset: util.BytesToUint32(data[:4]),
+		Size: util.BytesToUint32(data[4:])}, true
+}
+
+func (m cdbMap) Visit(visit func(NeedleValue) error) (err error) {
+	fh, err := os.Open(m.fn1)
+	if err != nil {
+		return fmt.Errorf("cannot open %s: %s", m.fn1, err)
+	}
+	defer fh.Close()
+	walk := func(elt cdb.Element) error {
+		if len(elt.Key) != 8 {
+			return nil
+		}
+		return visit(NeedleValue{Key: Key(util.BytesToUint64(elt.Key)),
+			Offset: util.BytesToUint32(elt.Data[:4]),
+			Size:   util.BytesToUint32(elt.Data[4:8])})
+	}
+	if err = cdb.DumpMap(fh, walk); err != nil {
+		return err
+	}
+	if m.c2 == nil {
+		return nil
+	}
+	fh.Close()
+	if fh, err = os.Open(m.fn2); err != nil {
+		return fmt.Errorf("cannot open %s: %s", m.fn2, err)
+	}
+	return cdb.DumpMap(fh, walk)
+}
+
+// converts an .idx index to a cdb
+func ConvertIndexToCdb(cdbName string, index *os.File) error {
+	idx, err := LoadNeedleMap(index)
+	if err != nil {
+		return fmt.Errorf("error loading needle map %s: %s", index, err)
+	}
+	defer idx.Close()
+	return DumpNeedleMapToCdb(cdbName, idx)
+}
+
+// dumps a NeedleMap into a cdb
+func DumpNeedleMapToCdb(cdbName string, nm *NeedleMap) error {
+	tempnam := cdbName + "t"
+	fnames := make([]string, 1, 2)
+	adder, closer, err := openTempCdb(tempnam)
+	if err != nil {
+		return fmt.Errorf("error creating factory: %s", err)
+	}
+	fnames[0] = tempnam
+
+	elt := cdb.Element{Key: make([]byte, 8), Data: make([]byte, 8)}
+
+	fcount := uint64(0)
+	walk := func(key uint64, offset, size uint32) error {
+		if fcount >= maxCdbRecCount {
+			if err = closer(); err != nil {
+				return err
+			}
+			tempnam = cdbName + "t2"
+			if adder, closer, err = openTempCdb(tempnam); err != nil {
+				return fmt.Errorf("error creating second factory: %s", err)
+			}
+			fnames = append(fnames, tempnam)
+			fcount = 0
+		}
+		util.Uint64toBytes(elt.Key, key)
+		util.Uint32toBytes(elt.Data[:4], offset)
+		util.Uint32toBytes(elt.Data[4:], size)
+		fcount++
+		return adder(elt)
+	}
+	// and write out the cdb from there
+	err = nm.Visit(func(nv NeedleValue) error {
+		return walk(uint64(nv.Key), nv.Offset, nv.Size)
+	})
+	if err != nil {
+		closer()
+		return fmt.Errorf("error walking index %s: %s", nm, err)
+	}
+	// store fileBytes
+	data, e := json.Marshal(nm.mapMetric)
+	if e != nil {
+		return fmt.Errorf("error marshaling metric %s: %s", nm.mapMetric, e)
+	}
+	if err = adder(cdb.Element{Key: []byte{'M'}, Data: data}); err != nil {
+		return err
+	}
+	if err = closer(); err != nil {
+		return err
+	}
+
+	os.Remove(cdbName)
+	if len(fnames) == 1 {
+		return os.Rename(fnames[0], cdbName)
+	}
+	bn, ext := nakeFilename(cdbName)
+	if err = os.Rename(fnames[0], bn+".1"+ext); err != nil {
+		return err
+	}
+	return os.Rename(fnames[1], bn+".2"+ext)
+}
+
+func openTempCdb(fileName string) (cdb.AdderFunc, cdb.CloserFunc, error) {
+	fh, err := os.Create(fileName)
+	if err != nil {
+		return nil, nil, fmt.Errorf("cannot create cdb file %s: %s", fileName, err)
+	}
+	adder, closer, err := cdb.MakeFactory(fh)
+	if err != nil {
+		fh.Close()
+		return nil, nil, fmt.Errorf("error creating factory: %s", err)
+	}
+	return adder, func() error {
+		if e := closer(); e != nil {
+			fh.Close()
+			return e
+		}
+		fh.Close()
+		return nil
+	}, nil
+}
+
+// returns filename without extension, and the extension
+func nakeFilename(fileName string) (string, string) {
+	ext := filepath.Ext(fileName)
+	return fileName[:len(fileName)-len(ext)], ext
+}
diff --git a/go/storage/cdb_map_test.go b/go/storage/cdb_map_test.go
new file mode 100644
index 000000000..e932a7ec5
--- /dev/null
+++ b/go/storage/cdb_map_test.go
@@ -0,0 +1,168 @@
+package storage
+
+import (
+	"log"
+	"math/rand"
+	"os"
+	"runtime"
+	"testing"
+)
+
+var testIndexFilename string = "../../test/sample.idx"
+
+func TestCdbMap0Convert(t *testing.T) {
+	indexFile, err := os.Open(testIndexFilename)
+	if err != nil {
+		t.Fatalf("cannot open %s: %s", testIndexFilename, err)
+	}
+	defer indexFile.Close()
+
+	cdbFn := testIndexFilename + ".cdb"
+	t.Logf("converting %s to %s", cdbFn, cdbFn)
+	if err = ConvertIndexToCdb(cdbFn, indexFile); err != nil {
+		t.Fatalf("error while converting: %s", err)
+	}
+}
+
+func TestCdbMap1Mem(t *testing.T) {
+	var nm NeedleMapper
+	i := 0
+	visit := func(nv NeedleValue) error {
+		i++
+		return nil
+	}
+
+	a := getMemStats()
+	t.Logf("opening %s.cdb", testIndexFilename)
+	nm, err := OpenCdbMap(testIndexFilename + ".cdb")
+	if err != nil {
+		t.Fatalf("error opening cdb: %s", err)
+	}
+	b := getMemStats()
+	log.Printf("opening cdb consumed %d bytes", b-a)
+	defer nm.Close()
+
+	a = getMemStats()
+	if err = nm.Visit(visit); err != nil {
+		t.Fatalf("error visiting %s: %s", nm, err)
+	}
+	b = getMemStats()
+	log.Printf("visit cdb %d consumed %d bytes", i, b-a)
+	nm.Close()
+
+	indexFile, err := os.Open(testIndexFilename)
+	if err != nil {
+		t.Fatalf("error opening idx: %s", err)
+	}
+	a = getMemStats()
+	nm, err = LoadNeedleMap(indexFile)
+	if err != nil {
+		t.Fatalf("error loading idx: %s", err)
+	}
+	defer nm.Close()
+	b = getMemStats()
+	log.Printf("opening idx consumed %d bytes", b-a)
+
+	i = 0
+	a = getMemStats()
+	if err = nm.Visit(visit); err != nil {
+		t.Fatalf("error visiting %s: %s", nm, err)
+	}
+	b = getMemStats()
+	log.Printf("visit idx %d consumed %d bytes", i, b-a)
+}
+
+func BenchmarkCdbMap9List(t *testing.B) {
+	t.StopTimer()
+	indexFile, err := os.Open(testIndexFilename)
+	if err != nil {
+		t.Fatalf("cannot open %s: %s", testIndexFilename, err)
+	}
+	defer indexFile.Close()
+
+	a := getMemStats()
+	t.Logf("opening %s", indexFile)
+	idx, err := LoadNeedleMap(indexFile)
+	if err != nil {
+		t.Fatalf("cannot load %s: %s", indexFile, err)
+	}
+	defer idx.Close()
+	b := getMemStats()
+	log.Printf("LoadNeedleMap consumed %d bytes", b-a)
+
+	cdbFn := testIndexFilename + ".cdb"
+	a = getMemStats()
+	t.Logf("opening %s", cdbFn)
+	m, err := OpenCdbMap(cdbFn)
+	if err != nil {
+		t.Fatalf("error opening %s: %s", cdbFn, err)
+	}
+	defer m.Close()
+	b = getMemStats()
+	log.Printf("OpenCdbMap consumed %d bytes", b-a)
+
+	i := 0
+	log.Printf("checking whether the cdb contains every key")
+	t.StartTimer()
+	err = idx.Visit(func(nv NeedleValue) error {
+		if i > t.N || rand.Intn(10) < 9 {
+			return nil
+		}
+		i++
+		if i%1000 == 0 {
+			log.Printf("%d. %s", i, nv)
+		}
+		if nv2, ok := m.Get(uint64(nv.Key)); !ok || nv2 == nil {
+			t.Errorf("%s in index, not in cdb", nv.Key)
+		} else if nv2.Key != nv.Key {
+			t.Errorf("requested key %d from cdb, got %d", nv.Key, nv2.Key)
+		} else if nv2.Offset != nv.Offset {
+			t.Errorf("offset is %d in index, %d in cdb", nv.Offset, nv2.Offset)
+		} else if nv2.Size != nv.Size {
+			t.Errorf("size is %d in index, %d in cdb", nv.Size, nv2.Size)
+		}
+		t.SetBytes(int64(nv.Size))
+		return nil
+	})
+	t.StopTimer()
+	if err != nil {
+		t.Errorf("error visiting index: %s", err)
+	}
+
+	i = 0
+	log.Printf("checking wheter the cdb contains no stray keys")
+	t.StartTimer()
+	err = m.Visit(func(nv NeedleValue) error {
+		if i > t.N || rand.Intn(10) < 9 {
+			return nil
+		}
+		if nv2, ok := m.Get(uint64(nv.Key)); !ok || nv2 == nil {
+			t.Errorf("%s in cdb, not in index", nv.Key)
+		} else if nv2.Key != nv.Key {
+			t.Errorf("requested key %d from index, got %d", nv.Key, nv2.Key)
+		} else if nv2.Offset != nv.Offset {
+			t.Errorf("offset is %d in cdb, %d in index", nv.Offset, nv2.Offset)
+		} else if nv2.Size != nv.Size {
+			t.Errorf("size is %d in cdb, %d in index", nv.Size, nv2.Size)
+		}
+		i++
+		if i%1000 == 0 {
+			log.Printf("%d. %s", i, nv)
+		}
+		t.SetBytes(int64(nv.Size))
+		return nil
+	})
+	t.StopTimer()
+	if err != nil {
+		t.Errorf("error visiting index: %s", err)
+	}
+}
+
+var mem = new(runtime.MemStats)
+
+// returns MemStats.Alloc after a GC
+func getMemStats() int64 {
+	runtime.GC()
+	runtime.ReadMemStats(mem)
+	return int64(mem.Alloc)
+}