diff --git a/weed/s3api/filer_util.go b/weed/s3api/filer_util.go
index 1c3814fce..b93b603e2 100644
--- a/weed/s3api/filer_util.go
+++ b/weed/s3api/filer_util.go
@@ -37,6 +37,7 @@ func (s3a *S3ApiServer) mkdir(ctx context.Context, parentDirectoryPath string, d
 
 		glog.V(1).Infof("mkdir: %v", request)
 		if _, err := client.CreateEntry(ctx, request); err != nil {
+			glog.V(0).Infof("mkdir %v: %v", request, err)
 			return fmt.Errorf("mkdir %s/%s: %v", parentDirectoryPath, dirName, err)
 		}
 
@@ -67,6 +68,7 @@ func (s3a *S3ApiServer) mkFile(ctx context.Context, parentDirectoryPath string,
 
 		glog.V(1).Infof("create file: %s/%s", parentDirectoryPath, fileName)
 		if _, err := client.CreateEntry(ctx, request); err != nil {
+			glog.V(0).Infof("create file %v:%v", request, err)
 			return fmt.Errorf("create file %s/%s: %v", parentDirectoryPath, fileName, err)
 		}
 
@@ -89,6 +91,7 @@ func (s3a *S3ApiServer) list(ctx context.Context, parentDirectoryPath, prefix, s
 		glog.V(4).Infof("read directory: %v", request)
 		resp, err := client.ListEntries(ctx, request)
 		if err != nil {
+			glog.V(0).Infof("read directory %v: %v", request, err)
 			return fmt.Errorf("list dir %v: %v", parentDirectoryPath, err)
 		}
 
@@ -114,6 +117,7 @@ func (s3a *S3ApiServer) rm(ctx context.Context, parentDirectoryPath string, entr
 
 		glog.V(1).Infof("delete entry %v/%v: %v", parentDirectoryPath, entryName, request)
 		if _, err := client.DeleteEntry(ctx, request); err != nil {
+			glog.V(0).Infof("delete entry %v: %v", request, err)
 			return fmt.Errorf("delete entry %s/%s: %v", parentDirectoryPath, entryName, err)
 		}
 
@@ -134,6 +138,7 @@ func (s3a *S3ApiServer) exists(ctx context.Context, parentDirectoryPath string,
 		glog.V(4).Infof("exists entry %v/%v: %v", parentDirectoryPath, entryName, request)
 		resp, err := client.LookupDirectoryEntry(ctx, request)
 		if err != nil {
+			glog.V(0).Infof("exists entry %v: %v", request, err)
 			return fmt.Errorf("exists entry %s/%s: %v", parentDirectoryPath, entryName, err)
 		}
 
diff --git a/weed/wdclient/vid_map.go b/weed/wdclient/vid_map.go
index 01d9cdaed..97df49cb6 100644
--- a/weed/wdclient/vid_map.go
+++ b/weed/wdclient/vid_map.go
@@ -3,15 +3,18 @@ package wdclient
 import (
 	"errors"
 	"fmt"
-	"math/rand"
 	"strconv"
 	"strings"
 	"sync"
-	"time"
+	"sync/atomic"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
 )
 
+const (
+	maxCursorIndex = 4096
+)
+
 type Location struct {
 	Url       string `json:"url,omitempty"`
 	PublicUrl string `json:"publicUrl,omitempty"`
@@ -20,14 +23,25 @@ type Location struct {
 type vidMap struct {
 	sync.RWMutex
 	vid2Locations map[uint32][]Location
-	r             *rand.Rand
+
+	cursor int32
 }
 
 func newVidMap() vidMap {
 	return vidMap{
 		vid2Locations: make(map[uint32][]Location),
-		r:             rand.New(rand.NewSource(time.Now().UnixNano())),
+		cursor:        -1,
+	}
+}
+
+func (vc *vidMap) getLocationIndex(length int) (int, error) {
+	if length <= 0 {
+		return 0, fmt.Errorf("invalid length: %d", length)
+	}
+	if atomic.LoadInt32(&vc.cursor) == maxCursorIndex {
+		atomic.CompareAndSwapInt32(&vc.cursor, maxCursorIndex, -1)
 	}
+	return int(atomic.AddInt32(&vc.cursor, 1)) % length, nil
 }
 
 func (vc *vidMap) LookupVolumeServerUrl(vid string) (serverUrl string, err error) {
@@ -94,7 +108,12 @@ func (vc *vidMap) GetRandomLocation(vid uint32) (serverUrl string, err error) {
 		return "", fmt.Errorf("volume %d not found", vid)
 	}
 
-	return locations[vc.r.Intn(len(locations))].Url, nil
+	index, err := vc.getLocationIndex(len(locations))
+	if err != nil {
+		return "", fmt.Errorf("volume %d: %v", vid, err)
+	}
+
+	return locations[index].Url, nil
 }
 
 func (vc *vidMap) addLocation(vid uint32, location Location) {
diff --git a/weed/wdclient/vid_map_test.go b/weed/wdclient/vid_map_test.go
new file mode 100644
index 000000000..87be2fc25
--- /dev/null
+++ b/weed/wdclient/vid_map_test.go
@@ -0,0 +1,76 @@
+package wdclient
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestLocationIndex(t *testing.T) {
+	vm := vidMap{}
+	// test must be failed
+	mustFailed := func(length int) {
+		_, err := vm.getLocationIndex(length)
+		if err == nil {
+			t.Errorf("length %d must be failed", length)
+		}
+		if err.Error() != fmt.Sprintf("invalid length: %d", length) {
+			t.Errorf("length %d must be failed. error: %v", length, err)
+		}
+	}
+
+	mustFailed(-1)
+	mustFailed(0)
+
+	mustOk := func(length, cursor, expect int) {
+		if length <= 0 {
+			t.Fatal("please don't do this")
+		}
+		vm.cursor = int32(cursor)
+		got, err := vm.getLocationIndex(length)
+		if err != nil {
+			t.Errorf("length: %d, why? %v\n", length, err)
+			return
+		}
+		if got != expect {
+			t.Errorf("cursor: %d, length: %d, expect: %d, got: %d\n", cursor, length, expect, got)
+			return
+		}
+	}
+
+	for i := -1; i < 100; i++ {
+		mustOk(7, i, (i+1)%7)
+	}
+
+	// when cursor reaches MaxInt64
+	mustOk(7, maxCursorIndex, 0)
+
+	// test with constructor
+	vm = newVidMap()
+	length := 7
+	for i := 0; i < 100; i++ {
+		got, err := vm.getLocationIndex(length)
+		if err != nil {
+			t.Errorf("length: %d, why? %v\n", length, err)
+			return
+		}
+		if got != i%length {
+			t.Errorf("length: %d, i: %d, got: %d\n", length, i, got)
+		}
+	}
+}
+
+func BenchmarkLocationIndex(b *testing.B) {
+	b.SetParallelism(8)
+	vm := vidMap{
+		cursor: maxCursorIndex - 4000,
+	}
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			_, err := vm.getLocationIndex(3)
+			if err != nil {
+				b.Error(err)
+			}
+		}
+	})
+}