diff --git a/Makefile b/Makefile
index be9c4d90b..c58519465 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,6 @@
 .PHONY: clean all test
 
 test:
-	go test -race ./...
 	for dir in cmd/* ; do \
 		(cd "$$dir"; go build -race) \
 	done
diff --git a/archiver.go b/archiver.go
index 15dbb3f43..4fa33819a 100644
--- a/archiver.go
+++ b/archiver.go
@@ -1,32 +1,75 @@
 package khepri
 
 import (
+	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
+	"sync"
 
 	"github.com/fd0/khepri/backend"
+	"github.com/fd0/khepri/chunker"
+)
+
+const (
+	maxConcurrentFiles = 32
+	maxConcurrentBlobs = 32
 )
 
 type Archiver struct {
-	be   backend.Server
-	key  *Key
-	ch   *ContentHandler
-	smap *StorageMap // blobs used for the current snapshot
+	be  backend.Server
+	key *Key
+	ch  *ContentHandler
+
+	bl *BlobList // blobs used for the current snapshot
+
+	fileToken chan struct{}
+	blobToken chan struct{}
+
+	Stats Stats
 
 	Error  func(dir string, fi os.FileInfo, err error) error
 	Filter func(item string, fi os.FileInfo) bool
+
+	ScannerUpdate func(stats Stats)
+	SaveUpdate    func(stats Stats)
+
+	sum sync.Mutex // for SaveUpdate
+}
+
+type Stats struct {
+	Files       int
+	Directories int
+	Other       int
+	Bytes       uint64
 }
 
 func NewArchiver(be backend.Server, key *Key) (*Archiver, error) {
 	var err error
-	arch := &Archiver{be: be, key: key}
+	arch := &Archiver{
+		be:        be,
+		key:       key,
+		fileToken: make(chan struct{}, maxConcurrentFiles),
+		blobToken: make(chan struct{}, maxConcurrentBlobs),
+	}
+
+	// fill file and blob token
+	for i := 0; i < maxConcurrentFiles; i++ {
+		arch.fileToken <- struct{}{}
+	}
+
+	for i := 0; i < maxConcurrentBlobs; i++ {
+		arch.blobToken <- struct{}{}
+	}
 
 	// abort on all errors
 	arch.Error = func(string, os.FileInfo, error) error { return err }
 	// allow all files
 	arch.Filter = func(string, os.FileInfo) bool { return true }
+	// do nothing
+	arch.ScannerUpdate = func(Stats) {}
 
-	arch.smap = NewStorageMap()
+	arch.bl = NewBlobList()
 	arch.ch, err = NewContentHandler(be, key)
 	if err != nil {
 		return nil, err
@@ -41,59 +84,124 @@ func NewArchiver(be backend.Server, key *Key) (*Archiver, error) {
 	return arch, nil
 }
 
-func (arch *Archiver) Save(t backend.Type, data []byte) (*Blob, error) {
+func (arch *Archiver) saveUpdate(stats Stats) {
+	if arch.SaveUpdate != nil {
+		arch.sum.Lock()
+		defer arch.sum.Unlock()
+		arch.SaveUpdate(stats)
+	}
+}
+
+func (arch *Archiver) Save(t backend.Type, data []byte) (Blob, error) {
 	blob, err := arch.ch.Save(t, data)
 	if err != nil {
-		return nil, err
+		return Blob{}, err
 	}
 
 	// store blob in storage map for current snapshot
-	arch.smap.Insert(blob)
+	arch.bl.Insert(blob)
 
 	return blob, nil
 }
 
-func (arch *Archiver) SaveJSON(t backend.Type, item interface{}) (*Blob, error) {
+func (arch *Archiver) SaveJSON(t backend.Type, item interface{}) (Blob, error) {
 	blob, err := arch.ch.SaveJSON(t, item)
 	if err != nil {
-		return nil, err
+		return Blob{}, err
 	}
 
 	// store blob in storage map for current snapshot
-	arch.smap.Insert(blob)
+	arch.bl.Insert(blob)
 
 	return blob, nil
 }
 
-func (arch *Archiver) SaveFile(node *Node) (Blobs, error) {
-	blobs, err := arch.ch.SaveFile(node.path, uint(node.Size))
+// SaveFile stores the content of the file on the backend as a Blob by calling
+// Save for each chunk.
+func (arch *Archiver) SaveFile(node *Node) error {
+	file, err := os.Open(node.path)
+	defer file.Close()
 	if err != nil {
-		return nil, arch.Error(node.path, nil, err)
+		return err
+	}
+
+	var blobs Blobs
+
+	// if the file is small enough, store it directly
+	if node.Size < chunker.MinSize {
+		buf, err := ioutil.ReadAll(file)
+		if err != nil {
+			return err
+		}
+
+		blob, err := arch.ch.Save(backend.Data, buf)
+		if err != nil {
+			return err
+		}
+
+		arch.saveUpdate(Stats{Bytes: blob.Size})
+
+		blobs = Blobs{blob}
+	} else {
+		// else store all chunks
+		chnker := chunker.New(file)
+		chans := [](<-chan Blob){}
+
+		for {
+			chunk, err := chnker.Next()
+			if err == io.EOF {
+				break
+			}
+
+			if err != nil {
+				return err
+			}
+
+			// acquire token, start goroutine to save chunk
+			token := <-arch.blobToken
+			resCh := make(chan Blob, 1)
+
+			go func(ch chan<- Blob) {
+				blob, err := arch.ch.Save(backend.Data, chunk.Data)
+				// TODO handle error
+				if err != nil {
+					panic(err)
+				}
+
+				arch.saveUpdate(Stats{Bytes: blob.Size})
+				arch.blobToken <- token
+				ch <- blob
+			}(resCh)
+
+			chans = append(chans, resCh)
+		}
+
+		blobs = []Blob{}
+		for _, ch := range chans {
+			blobs = append(blobs, <-ch)
+		}
 	}
 
 	node.Content = make([]backend.ID, len(blobs))
 	for i, blob := range blobs {
 		node.Content[i] = blob.ID
-		arch.smap.Insert(blob)
+		arch.bl.Insert(blob)
 	}
 
-	return blobs, err
+	return err
 }
 
-func (arch *Archiver) ImportDir(dir string) (Tree, error) {
+func (arch *Archiver) loadTree(dir string) (*Tree, error) {
+	// open and list path
 	fd, err := os.Open(dir)
 	defer fd.Close()
 	if err != nil {
-		return nil, arch.Error(dir, nil, err)
+		return nil, err
 	}
 
 	entries, err := fd.Readdir(-1)
 	if err != nil {
-		return nil, arch.Error(dir, nil, err)
-	}
-
-	if len(entries) == 0 {
-		return nil, nil
+		return nil, err
 	}
 
 	tree := Tree{}
@@ -107,71 +215,110 @@ func (arch *Archiver) ImportDir(dir string) (Tree, error) {
 
 		node, err := NodeFromFileInfo(path, entry)
 		if err != nil {
-			return nil, arch.Error(dir, entry, err)
+			// TODO: error processing
+			return nil, err
 		}
 
 		tree = append(tree, node)
 
 		if entry.IsDir() {
-			subtree, err := arch.ImportDir(path)
+			node.Tree, err = arch.loadTree(path)
 			if err != nil {
 				return nil, err
 			}
-
-			blob, err := arch.SaveJSON(backend.Tree, subtree)
-			if err != nil {
-				return nil, err
-			}
-
-			node.Subtree = blob.ID
-
-			continue
 		}
 
-		if node.Type == "file" {
-			_, err := arch.SaveFile(node)
-			if err != nil {
-				return nil, arch.Error(path, entry, err)
-			}
+		switch node.Type {
+		case "file":
+			arch.Stats.Files++
+			arch.Stats.Bytes += node.Size
+		case "dir":
+			arch.Stats.Directories++
+		default:
+			arch.Stats.Other++
 		}
 	}
 
-	return tree, nil
+	arch.ScannerUpdate(arch.Stats)
+
+	return &tree, nil
 }
 
-func (arch *Archiver) Import(dir string) (*Snapshot, *Blob, error) {
+func (arch *Archiver) LoadTree(path string) (*Tree, error) {
+	fi, err := os.Lstat(path)
+	if err != nil {
+		return nil, err
+	}
+
+	node, err := NodeFromFileInfo(path, fi)
+	if err != nil {
+		return nil, err
+	}
+
+	if node.Type != "dir" {
+		arch.Stats.Files = 1
+		arch.Stats.Bytes = node.Size
+		arch.ScannerUpdate(arch.Stats)
+		return &Tree{node}, nil
+	}
+
+	arch.Stats.Directories = 1
+	node.Tree, err = arch.loadTree(path)
+	if err != nil {
+		return nil, err
+	}
+
+	arch.ScannerUpdate(arch.Stats)
+
+	return &Tree{node}, nil
+}
+
+func (arch *Archiver) saveTree(t *Tree) (Blob, error) {
+	var wg sync.WaitGroup
+
+	for _, node := range *t {
+		if node.Tree != nil && node.Subtree == nil {
+			b, err := arch.saveTree(node.Tree)
+			if err != nil {
+				return Blob{}, err
+			}
+			node.Subtree = b.ID
+			arch.saveUpdate(Stats{Directories: 1})
+		} else if node.Type == "file" && len(node.Content) == 0 {
+			// start goroutine
+			wg.Add(1)
+			go func(n *Node) {
+				defer wg.Done()
+
+				// get token
+				token := <-arch.fileToken
+				defer func() {
+					arch.fileToken <- token
+				}()
+
+				// TODO: handle error
+				arch.SaveFile(n)
+				arch.saveUpdate(Stats{Files: 1})
+			}(node)
+		} else {
+			arch.saveUpdate(Stats{Other: 1})
+		}
+	}
+
+	wg.Wait()
+
+	blob, err := arch.SaveJSON(backend.Tree, t)
+	if err != nil {
+		return Blob{}, err
+	}
+
+	return blob, nil
+}
+
+func (arch *Archiver) Snapshot(dir string, t *Tree) (*Snapshot, backend.ID, error) {
 	sn := NewSnapshot(dir)
 
-	fi, err := os.Lstat(dir)
-	if err != nil {
-		return nil, nil, err
-	}
-
-	node, err := NodeFromFileInfo(dir, fi)
-	if err != nil {
-		return nil, nil, err
-	}
-
-	if node.Type == "dir" {
-		tree, err := arch.ImportDir(dir)
-		if err != nil {
-			return nil, nil, err
-		}
-
-		blob, err := arch.SaveJSON(backend.Tree, tree)
-		if err != nil {
-			return nil, nil, err
-		}
-
-		node.Subtree = blob.ID
-	} else if node.Type == "file" {
-		_, err := arch.SaveFile(node)
-		if err != nil {
-			return nil, nil, err
-		}
-	}
-
-	blob, err := arch.SaveJSON(backend.Tree, &Tree{node})
+	blob, err := arch.saveTree(t)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -179,11 +326,11 @@ func (arch *Archiver) Import(dir string) (*Snapshot, *Blob, error) {
 	sn.Content = blob.ID
 
 	// save snapshot
-	sn.StorageMap = arch.smap
+	sn.BlobList = arch.bl
 	blob, err = arch.SaveJSON(backend.Snapshot, sn)
 	if err != nil {
 		return nil, nil, err
 	}
 
-	return sn, blob, nil
+	return sn, blob.Storage, nil
 }
diff --git a/archiver_test.go b/archiver_test.go
new file mode 100644
index 000000000..529b2bb5f
--- /dev/null
+++ b/archiver_test.go
@@ -0,0 +1,53 @@
+package khepri_test
+
+import (
+	"bytes"
+	"io"
+	"math/rand"
+	"testing"
+
+	"github.com/fd0/khepri/chunker"
+)
+
+func get_random(seed, count int) []byte {
+	buf := make([]byte, count)
+
+	rnd := rand.New(rand.NewSource(23))
+	for i := 0; i < count; i += 4 {
+		r := rnd.Uint32()
+		buf[i] = byte(r)
+		buf[i+1] = byte(r >> 8)
+		buf[i+2] = byte(r >> 16)
+		buf[i+3] = byte(r >> 24)
+	}
+
+	return buf
+}
+
+func BenchmarkChunkEncrypt(b *testing.B) {
+	data := get_random(23, 10<<20) // 10MiB
+
+	be := setupBackend(b)
+	defer teardownBackend(b, be)
+	key := setupKey(b, be, "geheim")
+
+	b.ResetTimer()
+	b.SetBytes(int64(len(data)))
+
+	for i := 0; i < b.N; i++ {
+		ch := chunker.New(bytes.NewReader(data))
+
+		for {
+			chunk_data, err := ch.Next()
+
+			if err == io.EOF {
+				break
+			}
+
+			ok(b, err)
+
+			_, err = key.Encrypt(chunk_data.Data)
+			ok(b, err)
+		}
+	}
+}
diff --git a/backend/id.go b/backend/id.go
index ef9067040..0c15cad26 100644
--- a/backend/id.go
+++ b/backend/id.go
@@ -47,6 +47,11 @@ func (id ID) EqualString(other string) (bool, error) {
 	return id.Equal(ID(s)), nil
 }
 
+// Compare compares this ID to another one, returning -1, 0, or 1.
+func (id ID) Compare(other ID) int {
+	return bytes.Compare(other, id)
+}
+
 func (id ID) MarshalJSON() ([]byte, error) {
 	return json.Marshal(id.String())
 }
diff --git a/bloblist.go b/bloblist.go
new file mode 100644
index 000000000..48820e95f
--- /dev/null
+++ b/bloblist.go
@@ -0,0 +1,99 @@
+package khepri
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"sort"
+	"sync"
+)
+
+type BlobList struct {
+	list []Blob
+	m    sync.Mutex
+}
+
+var ErrBlobNotFound = errors.New("Blob not found")
+
+func NewBlobList() *BlobList {
+	return &BlobList{
+		list: []Blob{},
+	}
+}
+
+func (bl *BlobList) find(blob Blob) (int, Blob, error) {
+	pos := sort.Search(len(bl.list), func(i int) bool {
+		return blob.ID.Compare(bl.list[i].ID) >= 0
+	})
+
+	if pos < len(bl.list) && blob.ID.Compare(bl.list[pos].ID) == 0 {
+		return pos, bl.list[pos], nil
+	}
+
+	return pos, Blob{}, ErrBlobNotFound
+}
+
+func (bl *BlobList) Find(blob Blob) (Blob, error) {
+	bl.m.Lock()
+	defer bl.m.Unlock()
+
+	_, blob, err := bl.find(blob)
+	return blob, err
+}
+
+func (bl *BlobList) Merge(other *BlobList) {
+	bl.m.Lock()
+	defer bl.m.Unlock()
+	other.m.Lock()
+	defer other.m.Unlock()
+
+	for _, blob := range other.list {
+		bl.insert(blob)
+	}
+}
+
+func (bl *BlobList) insert(blob Blob) {
+	pos, _, err := bl.find(blob)
+	if err == nil {
+		// already present
+		return
+	}
+
+	// insert blob
+	// https://code.google.com/p/go-wiki/wiki/bliceTricks
+	bl.list = append(bl.list, Blob{})
+	copy(bl.list[pos+1:], bl.list[pos:])
+	bl.list[pos] = blob
+}
+
+func (bl *BlobList) Insert(blob Blob) {
+	bl.m.Lock()
+	defer bl.m.Unlock()
+
+	bl.insert(blob)
+}
+
+func (bl BlobList) MarshalJSON() ([]byte, error) {
+	return json.Marshal(bl.list)
+}
+
+func (bl *BlobList) UnmarshalJSON(data []byte) error {
+	return json.Unmarshal(data, &bl.list)
+}
+
+// Compare compares two blobs by comparing the ID and the size. It returns -1,
+// 0, or 1.
+func (blob Blob) Compare(other Blob) int {
+	if res := bytes.Compare(other.ID, blob.ID); res != 0 {
+		return res
+	}
+
+	if blob.Size < other.Size {
+		return -1
+	}
+	if blob.Size > other.Size {
+		return 1
+	}
+
+	return 0
+}
diff --git a/bloblist_test.go b/bloblist_test.go
new file mode 100644
index 000000000..3add85cf9
--- /dev/null
+++ b/bloblist_test.go
@@ -0,0 +1,137 @@
+package khepri_test
+
+import (
+	"crypto/rand"
+	"encoding/json"
+	"flag"
+	"io"
+	mrand "math/rand"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/fd0/khepri"
+)
+
+const backendIDSize = 8
+
+var maxWorkers = flag.Uint("workers", 100, "number of workers to test BlobList concurrent access against")
+
+func randomID() []byte {
+	buf := make([]byte, backendIDSize)
+	_, err := io.ReadFull(rand.Reader, buf)
+	if err != nil {
+		panic(err)
+	}
+	return buf
+}
+
+func newBlob() khepri.Blob {
+	return khepri.Blob{ID: randomID(), Size: uint64(mrand.Uint32())}
+}
+
+// Test basic functionality
+func TestBlobList(t *testing.T) {
+	bl := khepri.NewBlobList()
+
+	b := newBlob()
+	bl.Insert(b)
+
+	for i := 0; i < 1000; i++ {
+		bl.Insert(newBlob())
+	}
+
+	b2, err := bl.Find(khepri.Blob{ID: b.ID})
+	ok(t, err)
+	assert(t, b2.Compare(b) == 0, "items are not equal: want %v, got %v", b, b2)
+
+	bl2 := khepri.NewBlobList()
+	for i := 0; i < 1000; i++ {
+		bl.Insert(newBlob())
+	}
+
+	b2, err = bl2.Find(b)
+	assert(t, err != nil, "found ID in khepri that was never inserted: %v", b2)
+
+	bl2.Merge(bl)
+
+	b2, err = bl2.Find(b)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if b.Compare(b2) != 0 {
+		t.Fatalf("items are not equal: want %v, got %v", b, b2)
+	}
+}
+
+// Test JSON encode/decode
+func TestBlobListJSON(t *testing.T) {
+	bl := khepri.NewBlobList()
+	b := khepri.Blob{ID: []byte{1, 2, 3, 4}}
+	bl.Insert(b)
+
+	b2, err := bl.Find(b)
+	ok(t, err)
+	assert(t, b2.Compare(b) == 0, "items are not equal: want %v, got %v", b, b2)
+
+	buf, err := json.Marshal(bl)
+	ok(t, err)
+
+	bl2 := khepri.BlobList{}
+	json.Unmarshal(buf, &bl2)
+
+	b2, err = bl2.Find(b)
+	ok(t, err)
+	assert(t, b2.Compare(b) == 0, "items are not equal: want %v, got %v", b, b2)
+
+	buf, err = json.Marshal(bl2)
+	ok(t, err)
+}
+
+// random insert/find access by several goroutines
+func TestBlobListRandom(t *testing.T) {
+	var wg sync.WaitGroup
+
+	worker := func(bl *khepri.BlobList) {
+		defer wg.Done()
+
+		b := newBlob()
+		bl.Insert(b)
+
+		for i := 0; i < 200; i++ {
+			bl.Insert(newBlob())
+		}
+
+		d := time.Duration(mrand.Intn(10)*100) * time.Millisecond
+		time.Sleep(d)
+
+		for i := 0; i < 100; i++ {
+			b2, err := bl.Find(b)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if b.Compare(b2) != 0 {
+				t.Fatalf("items are not equal: want %v, got %v", b, b2)
+			}
+		}
+
+		bl2 := khepri.NewBlobList()
+		for i := 0; i < 200; i++ {
+			bl2.Insert(newBlob())
+		}
+
+		bl2.Merge(bl)
+	}
+
+	bl := khepri.NewBlobList()
+
+	for i := 0; uint(i) < *maxWorkers; i++ {
+		wg.Add(1)
+		go worker(bl)
+	}
+
+	wg.Wait()
+}
diff --git a/chunker/chunker.go b/chunker/chunker.go
index c317672c0..2cd5a4e34 100644
--- a/chunker/chunker.go
+++ b/chunker/chunker.go
@@ -218,8 +218,6 @@ func (c *chunker) Next() (*Chunk, error) {
 		c.pos += steps
 		c.bpos = c.bmax
 	}
-
-	return nil, nil
 }
 
 func (c *chunker) append(b byte) {
diff --git a/cmd/khepri/.gitignore b/cmd/khepri/.gitignore
new file mode 100644
index 000000000..aee2e4ce1
--- /dev/null
+++ b/cmd/khepri/.gitignore
@@ -0,0 +1 @@
+config.mk
diff --git a/cmd/khepri/Makefile b/cmd/khepri/Makefile
index dab9cbb16..66819e525 100644
--- a/cmd/khepri/Makefile
+++ b/cmd/khepri/Makefile
@@ -6,12 +6,15 @@ TAGS =
 
 .PHONY: all clean debug
 
+# include config file if it exists
+-include $(CURDIR)/config.mk
+
 all: khepri
 
-khepri: *.go
+khepri: *.go $(wildcard ../../*.go) $(wildcard ../../*/*.go)
 	go build $(TAGS) -ldflags "$(LDFLAGS)"
 
-debug: TAGS=-tags debug
+debug: TAGS=-tags debug_cmd
 debug: khepri
 
 clean:
diff --git a/cmd/khepri/cmd_backup.go b/cmd/khepri/cmd_backup.go
index 6fdc6c761..0e3972186 100644
--- a/cmd/khepri/cmd_backup.go
+++ b/cmd/khepri/cmd_backup.go
@@ -4,11 +4,42 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"strings"
+	"time"
 
 	"github.com/fd0/khepri"
 	"github.com/fd0/khepri/backend"
+	"golang.org/x/crypto/ssh/terminal"
 )
 
+func format_bytes(c uint64) string {
+	b := float64(c)
+
+	switch {
+	case c > 1<<40:
+		return fmt.Sprintf("%.3f TiB", b/(1<<40))
+	case c > 1<<30:
+		return fmt.Sprintf("%.3f GiB", b/(1<<30))
+	case c > 1<<20:
+		return fmt.Sprintf("%.3f MiB", b/(1<<20))
+	case c > 1<<10:
+		return fmt.Sprintf("%.3f KiB", b/(1<<10))
+	default:
+		return fmt.Sprintf("%d B", c)
+	}
+}
+
+func print_tree2(indent int, t *khepri.Tree) {
+	for _, node := range *t {
+		if node.Tree != nil {
+			fmt.Printf("%s%s/\n", strings.Repeat("  ", indent), node.Name)
+			print_tree2(indent+1, node.Tree)
+		} else {
+			fmt.Printf("%s%s\n", strings.Repeat("  ", indent), node.Name)
+		}
+	}
+}
+
 func commandBackup(be backend.Server, key *khepri.Key, args []string) error {
 	if len(args) != 1 {
 		return errors.New("usage: backup [dir|file]")
@@ -25,12 +56,52 @@ func commandBackup(be backend.Server, key *khepri.Key, args []string) error {
 		return err
 	}
 
-	_, blob, err := arch.Import(target)
+	fmt.Printf("scanning %s\n", target)
+
+	if terminal.IsTerminal(int(os.Stdout.Fd())) {
+		arch.ScannerUpdate = func(stats khepri.Stats) {
+			fmt.Printf("\r%6d directories, %6d files, %14s", stats.Directories, stats.Files, format_bytes(stats.Bytes))
+		}
+	}
+
+	// TODO: add filter
+	// arch.Filter = func(dir string, fi os.FileInfo) bool {
+	// 	return true
+	// }
+
+	t, err := arch.LoadTree(target)
 	if err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
 		return err
 	}
 
-	fmt.Printf("snapshot %s saved\n", blob.Storage)
+	fmt.Printf("\r%6d directories, %6d files, %14s\n", arch.Stats.Directories, arch.Stats.Files, format_bytes(arch.Stats.Bytes))
+
+	stats := khepri.Stats{}
+	if terminal.IsTerminal(int(os.Stdout.Fd())) {
+		arch.SaveUpdate = func(s khepri.Stats) {
+			stats.Files += s.Files
+			stats.Directories += s.Directories
+			stats.Other += s.Other
+			stats.Bytes += s.Bytes
+
+			fmt.Printf("\r%3.2f%% %d/%d directories, %d/%d files, %s/%s",
+				float64(stats.Bytes)/float64(arch.Stats.Bytes)*100,
+				stats.Directories, arch.Stats.Directories,
+				stats.Files, arch.Stats.Files,
+				format_bytes(stats.Bytes), format_bytes(arch.Stats.Bytes))
+		}
+	}
+
+	start := time.Now()
+	sn, id, err := arch.Snapshot(target, t)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+	}
+
+	fmt.Printf("\nsnapshot %s saved: %v\n", id, sn)
+	duration := time.Now().Sub(start)
+	fmt.Printf("duration: %s, %.2fMiB/s\n", duration, float64(arch.Stats.Bytes)/float64(duration/time.Second)/(1<<20))
 
 	return nil
 }
diff --git a/cmd/khepri/debug.go b/cmd/khepri/debug.go
index 687f0f162..dc978a51a 100644
--- a/cmd/khepri/debug.go
+++ b/cmd/khepri/debug.go
@@ -1,4 +1,4 @@
-// +build debug
+// +build debug_cmd
 
 package main
 
@@ -17,8 +17,8 @@ func initDebugLogger() *log.Logger {
 	// create new log file
 	filename := fmt.Sprintf("khepri-debug-%d-%s",
 		os.Getpid(), time.Now().Format("20060201-150405"))
-	f, err := os.OpenFile(filepath.Join(os.TempDir(), filename),
-		os.O_WRONLY|os.O_CREATE, 0600)
+	path := filepath.Join(os.TempDir(), filename)
+	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE, 0600)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "unable to create debug log file: %v", err)
 		os.Exit(2)
@@ -26,7 +26,7 @@ func initDebugLogger() *log.Logger {
 
 	// open logger
 	l := log.New(io.MultiWriter(os.Stderr, f), "DEBUG: ", log.LstdFlags)
-	fmt.Fprintf(os.Stderr, "logging activated, writing log file %s", filename)
+	fmt.Fprintf(os.Stderr, "debug log for khepri command activated, writing log file %s\n", path)
 	l.Printf("khepri %s", version)
 
 	return l
diff --git a/cmd/khepri/debug_release.go b/cmd/khepri/debug_release.go
index 77f5c1b76..ef42f0638 100644
--- a/cmd/khepri/debug_release.go
+++ b/cmd/khepri/debug_release.go
@@ -1,4 +1,4 @@
-// +build !debug
+// +build !debug_cmd
 
 package main
 
diff --git a/cmd/khepri/main.go b/cmd/khepri/main.go
index 719a84ee8..cd1c0a777 100644
--- a/cmd/khepri/main.go
+++ b/cmd/khepri/main.go
@@ -5,6 +5,7 @@ import (
 	"log"
 	"net/url"
 	"os"
+	"runtime"
 	"sort"
 	"strings"
 
@@ -128,6 +129,9 @@ func init() {
 	commands["snapshots"] = commandSnapshots
 	commands["cat"] = commandCat
 	commands["ls"] = commandLs
+
+	// set GOMAXPROCS to number of CPUs
+	runtime.GOMAXPROCS(runtime.NumCPU())
 }
 
 func main() {
diff --git a/contenthandler.go b/contenthandler.go
index 271df9b76..625261993 100644
--- a/contenthandler.go
+++ b/contenthandler.go
@@ -3,27 +3,24 @@ package khepri
 import (
 	"encoding/json"
 	"errors"
-	"io"
-	"io/ioutil"
-	"os"
+	"fmt"
 
 	"github.com/fd0/khepri/backend"
-	"github.com/fd0/khepri/chunker"
 )
 
 type ContentHandler struct {
 	be  backend.Server
 	key *Key
 
-	content *StorageMap
+	bl *BlobList
 }
 
 // NewContentHandler creates a new content handler.
 func NewContentHandler(be backend.Server, key *Key) (*ContentHandler, error) {
 	ch := &ContentHandler{
-		be:      be,
-		key:     key,
-		content: NewStorageMap(),
+		be:  be,
+		key: key,
+		bl:  NewBlobList(),
 	}
 
 	return ch, nil
@@ -36,7 +33,8 @@ func (ch *ContentHandler) LoadSnapshot(id backend.ID) (*Snapshot, error) {
 		return nil, err
 	}
 
-	ch.content.Merge(sn.StorageMap)
+	ch.bl.Merge(sn.BlobList)
+
 	return sn, nil
 }
 
@@ -49,7 +47,8 @@ func (ch *ContentHandler) LoadAllSnapshots() error {
 		if err != nil {
 			return
 		}
-		ch.content.Merge(sn.StorageMap)
+
+		ch.bl.Merge(sn.BlobList)
 	})
 	if err != nil {
 		return err
@@ -60,18 +59,18 @@ func (ch *ContentHandler) LoadAllSnapshots() error {
 
 // Save encrypts data and stores it to the backend as type t. If the data was
 // already saved before, the blob is returned.
-func (ch *ContentHandler) Save(t backend.Type, data []byte) (*Blob, error) {
+func (ch *ContentHandler) Save(t backend.Type, data []byte) (Blob, error) {
 	// compute plaintext hash
 	id := backend.Hash(data)
 
 	// test if the hash is already in the backend
-	blob := ch.content.Find(id)
-	if blob != nil {
+	blob, err := ch.bl.Find(Blob{ID: id})
+	if err == nil {
 		return blob, nil
 	}
 
 	// else create a new blob
-	blob = &Blob{
+	blob = Blob{
 		ID:   id,
 		Size: uint64(len(data)),
 	}
@@ -79,85 +78,36 @@ func (ch *ContentHandler) Save(t backend.Type, data []byte) (*Blob, error) {
 	// encrypt blob
 	ciphertext, err := ch.key.Encrypt(data)
 	if err != nil {
-		return nil, err
+		return Blob{}, err
 	}
 
 	// save blob
 	sid, err := ch.be.Create(t, ciphertext)
 	if err != nil {
-		return nil, err
+		return Blob{}, err
 	}
 
 	blob.Storage = sid
 	blob.StorageSize = uint64(len(ciphertext))
 
 	// insert blob into the storage map
-	ch.content.Insert(blob)
+	ch.bl.Insert(blob)
 
 	return blob, nil
 }
 
 // SaveJSON serialises item as JSON and uses Save() to store it to the backend as type t.
-func (ch *ContentHandler) SaveJSON(t backend.Type, item interface{}) (*Blob, error) {
+func (ch *ContentHandler) SaveJSON(t backend.Type, item interface{}) (Blob, error) {
 	// convert to json
 	data, err := json.Marshal(item)
 	if err != nil {
-		return nil, err
+		return Blob{}, err
 	}
 
 	// compress and save data
 	return ch.Save(t, backend.Compress(data))
 }
 
-// SaveFile stores the content of the file on the backend as a Blob by calling
-// Save for each chunk.
-func (ch *ContentHandler) SaveFile(filename string, size uint) (Blobs, error) {
-	file, err := os.Open(filename)
-	defer file.Close()
-	if err != nil {
-		return nil, err
-	}
-
-	// if the file is small enough, store it directly
-	if size < chunker.MinSize {
-		buf, err := ioutil.ReadAll(file)
-		if err != nil {
-			return nil, err
-		}
-
-		blob, err := ch.Save(backend.Data, buf)
-		if err != nil {
-			return nil, err
-		}
-
-		return Blobs{blob}, nil
-	}
-
-	// else store all chunks
-	blobs := Blobs{}
-	chunker := chunker.New(file)
-
-	for {
-		chunk, err := chunker.Next()
-		if err == io.EOF {
-			break
-		}
-
-		if err != nil {
-			return nil, err
-		}
-
-		blob, err := ch.Save(backend.Data, chunk.Data)
-		if err != nil {
-			return nil, err
-		}
-
-		blobs = append(blobs, blob)
-	}
-
-	return blobs, nil
-}
-
 // Load tries to load and decrypt content identified by t and id from the backend.
 func (ch *ContentHandler) Load(t backend.Type, id backend.ID) ([]byte, error) {
 	if t == backend.Snapshot {
@@ -177,9 +127,9 @@ func (ch *ContentHandler) Load(t backend.Type, id backend.ID) ([]byte, error) {
 	}
 
 	// lookup storage hash
-	blob := ch.content.Find(id)
-	if blob == nil {
-		return nil, errors.New("Storage ID not found")
+	blob, err := ch.bl.Find(Blob{ID: id})
+	if err != nil {
+		return nil, fmt.Errorf("Storage ID %s not found", id)
 	}
 
 	// load data
diff --git a/debug.go b/debug.go
new file mode 100644
index 000000000..80952b3e7
--- /dev/null
+++ b/debug.go
@@ -0,0 +1,36 @@
+// +build debug
+
+package khepri
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+var debugLogger = initDebugLogger()
+
+func initDebugLogger() *log.Logger {
+	// create new log file
+	filename := fmt.Sprintf("khepri-lib-debug-%d-%s",
+		os.Getpid(), time.Now().Format("20060201-150405"))
+	path := filepath.Join(os.TempDir(), filename)
+	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE, 0600)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "unable to create debug log file: %v", err)
+		os.Exit(2)
+	}
+
+	// open logger
+	l := log.New(io.MultiWriter(os.Stderr, f), "DEBUG: ", log.LstdFlags)
+	fmt.Fprintf(os.Stderr, "debug log for khepri library activated, writing log file %s\n", path)
+
+	return l
+}
+
+func debug(fmt string, args ...interface{}) {
+	debugLogger.Printf(fmt, args...)
+}
diff --git a/debug_release.go b/debug_release.go
new file mode 100644
index 000000000..21f2b24a5
--- /dev/null
+++ b/debug_release.go
@@ -0,0 +1,5 @@
+// +build !debug
+
+package khepri
+
+func debug(fmt string, args ...interface{}) {}
diff --git a/restorer.go b/restorer.go
index 8e94f5411..c1717db3f 100644
--- a/restorer.go
+++ b/restorer.go
@@ -30,12 +30,12 @@ func NewRestorer(be backend.Server, key *Key, snid backend.ID) (*Restorer, error
 	var err error
 	r.ch, err = NewContentHandler(be, key)
 	if err != nil {
-		return nil, err
+		return nil, arrar.Annotate(err, "create contenthandler for restorer")
 	}
 
 	r.sn, err = r.ch.LoadSnapshot(snid)
 	if err != nil {
-		return nil, err
+		return nil, arrar.Annotate(err, "load snapshot for restorer")
 	}
 
 	// abort on all errors
diff --git a/snapshot.go b/snapshot.go
index fa7d10e1d..c0cc6c2bb 100644
--- a/snapshot.go
+++ b/snapshot.go
@@ -11,14 +11,14 @@ import (
 )
 
 type Snapshot struct {
-	Time       time.Time   `json:"time"`
-	Content    backend.ID  `json:"content"`
-	StorageMap *StorageMap `json:"map"`
-	Dir        string      `json:"dir"`
-	Hostname   string      `json:"hostname,omitempty"`
-	Username   string      `json:"username,omitempty"`
-	UID        string      `json:"uid,omitempty"`
-	GID        string      `json:"gid,omitempty"`
+	Time     time.Time  `json:"time"`
+	Content  backend.ID `json:"content"`
+	BlobList *BlobList  `json:"blobs"`
+	Dir      string     `json:"dir"`
+	Hostname string     `json:"hostname,omitempty"`
+	Username string     `json:"username,omitempty"`
+	UID      string     `json:"uid,omitempty"`
+	GID      string     `json:"gid,omitempty"`
 
 	id backend.ID // plaintext ID, used during restore
 }
diff --git a/storagemap.go b/storagemap.go
deleted file mode 100644
index db77952e2..000000000
--- a/storagemap.go
+++ /dev/null
@@ -1,51 +0,0 @@
-package khepri
-
-import (
-	"bytes"
-	"sort"
-
-	"github.com/fd0/khepri/backend"
-)
-
-type StorageMap Blobs
-
-func NewStorageMap() *StorageMap {
-	return &StorageMap{}
-}
-
-func (m StorageMap) find(id backend.ID) (int, *Blob) {
-	i := sort.Search(len(m), func(i int) bool {
-		return bytes.Compare(m[i].ID, id) >= 0
-	})
-
-	if i < len(m) && bytes.Equal(m[i].ID, id) {
-		return i, m[i]
-	}
-
-	return i, nil
-}
-
-func (m StorageMap) Find(id backend.ID) *Blob {
-	_, blob := m.find(id)
-	return blob
-}
-
-func (m *StorageMap) Insert(blob *Blob) {
-	pos, b := m.find(blob.ID)
-	if b != nil {
-		// already present
-		return
-	}
-
-	// insert blob
-	// https://code.google.com/p/go-wiki/wiki/SliceTricks
-	*m = append(*m, nil)
-	copy((*m)[pos+1:], (*m)[pos:])
-	(*m)[pos] = blob
-}
-
-func (m *StorageMap) Merge(sm *StorageMap) {
-	for _, blob := range *sm {
-		m.Insert(blob)
-	}
-}
diff --git a/tree.go b/tree.go
index ad5f64597..0aa41a44d 100644
--- a/tree.go
+++ b/tree.go
@@ -34,6 +34,8 @@ type Node struct {
 	Content    []backend.ID `json:"content,omitempty"`
 	Subtree    backend.ID   `json:"subtree,omitempty"`
 
+	Tree *Tree `json:"-"`
+
 	path string
 }
 
@@ -44,7 +46,7 @@ type Blob struct {
 	StorageSize uint64     `json:"ssize,omitempty"` // encrypted Size
 }
 
-type Blobs []*Blob
+type Blobs []Blob
 
 func (n Node) String() string {
 	switch n.Type {