read from alternative replica

related to https://github.com/chrislusf/seaweedfs/issues/1512

12 files changed, 182 insertions, 147 deletions

diff --git a/weed/command/benchmark.go b/weed/command/benchmark.go
index 4a9a9619a..8bb585d91 100644
--- a/weed/command/benchmark.go
+++ b/weed/command/benchmark.go
@@ -282,14 +282,19 @@ func readFiles(fileIdLineChan chan string, s *stat) {
 		start := time.Now()
 		var bytesRead int
 		var err error
-		url, err := b.masterClient.LookupFileId(fid)
+		urls, err := b.masterClient.LookupFileId(fid)
 		if err != nil {
 			s.failed++
 			println("!!!! ", fid, " location not found!!!!!")
 			continue
 		}
 		var bytes []byte
-		bytes, err = util.Get(url)
+		for _, url := range urls {
+			bytes, err = util.Get(url)
+			if err == nil {
+				break
+			}
+		}
 		bytesRead = len(bytes)
 		if err == nil {
 			s.completed++
diff --git a/weed/filer/filechunk_manifest.go b/weed/filer/filechunk_manifest.go
index 37b172357..6fcd7abc2 100644
--- a/weed/filer/filechunk_manifest.go
+++ b/weed/filer/filechunk_manifest.go
@@ -84,21 +84,26 @@ func ResolveOneChunkManifest(lookupFileIdFn LookupFileIdFunctionType, chunk *fil
 
 // TODO fetch from cache for weed mount?
 func fetchChunk(lookupFileIdFn LookupFileIdFunctionType, fileId string, cipherKey []byte, isGzipped bool) ([]byte, error) {
-	urlString, err := lookupFileIdFn(fileId)
+	urlStrings, err := lookupFileIdFn(fileId)
 	if err != nil {
 		glog.Errorf("operation LookupFileId %s failed, err: %v", fileId, err)
 		return nil, err
 	}
 	var buffer bytes.Buffer
-	err = util.ReadUrlAsStream(urlString, cipherKey, isGzipped, true, 0, 0, func(data []byte) {
-		buffer.Write(data)
-	})
-	if err != nil {
-		glog.V(0).Infof("read %s failed, err: %v", fileId, err)
-		return nil, err
+
+	for _, urlString := range urlStrings {
+		err = util.ReadUrlAsStream(urlString, cipherKey, isGzipped, true, 0, 0, func(data []byte) {
+			buffer.Write(data)
+		})
+		if err != nil {
+			glog.V(0).Infof("read %s failed, err: %v", fileId, err)
+			buffer.Reset()
+		} else {
+			break
+		}
 	}
 
-	return buffer.Bytes(), nil
+	return buffer.Bytes(), err
 }
 
 func MaybeManifestize(saveFunc SaveDataAsChunkFunctionType, inputChunks []*filer_pb.FileChunk) (chunks []*filer_pb.FileChunk, err error) {
diff --git a/weed/filer/reader_at.go b/weed/filer/reader_at.go
index 3aeb9a94d..74f037557 100644
--- a/weed/filer/reader_at.go
+++ b/weed/filer/reader_at.go
@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"github.com/golang/groupcache/singleflight"
 	"io"
-	"math/rand"
 	"sync"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
@@ -17,24 +16,24 @@ import (
 type ChunkReadAt struct {
 	masterClient *wdclient.MasterClient
 	chunkViews   []*ChunkView
-	lookupFileId func(fileId string) (targetUrl string, err error)
+	lookupFileId LookupFileIdFunctionType
 	readerLock   sync.Mutex
 	fileSize     int64
 
-	fetchGroup          singleflight.Group
-	lastChunkFileId     string
-	lastChunkData       []byte
-	chunkCache          chunk_cache.ChunkCache
+	fetchGroup      singleflight.Group
+	lastChunkFileId string
+	lastChunkData   []byte
+	chunkCache      chunk_cache.ChunkCache
 }
 
 // var _ = io.ReaderAt(&ChunkReadAt{})
 
-type LookupFileIdFunctionType func(fileId string) (targetUrl string, err error)
+type LookupFileIdFunctionType func(fileId string) (targetUrls []string, err error)
 
 func LookupFn(filerClient filer_pb.FilerClient) LookupFileIdFunctionType {
 
 	vidCache := make(map[string]*filer_pb.Locations)
-	return func(fileId string) (targetUrl string, err error) {
+	return func(fileId string) (targetUrls []string, err error) {
 		vid := VolumeId(fileId)
 		locations, found := vidCache[vid]
 
@@ -59,8 +58,11 @@ func LookupFn(filerClient filer_pb.FilerClient) LookupFileIdFunctionType {
 			})
 		}
 
-		volumeServerAddress := filerClient.AdjustedUrl(locations.Locations[rand.Intn(len(locations.Locations))].Url)
-		targetUrl = fmt.Sprintf("http://%s/%s", volumeServerAddress, fileId)
+		for _, loc := range locations.Locations {
+			volumeServerAddress := filerClient.AdjustedUrl(loc.Url)
+			targetUrl := fmt.Sprintf("http://%s/%s", volumeServerAddress, fileId)
+			targetUrls = append(targetUrls, targetUrl)
+		}
 
 		return
 	}
@@ -142,7 +144,7 @@ func (c *ChunkReadAt) doReadAt(p []byte, offset int64) (n int, err error) {
 
 }
 
-func (c *ChunkReadAt) readFromWholeChunkData(chunkView *ChunkView, nextChunkViews... *ChunkView) (chunkData []byte, err error) {
+func (c *ChunkReadAt) readFromWholeChunkData(chunkView *ChunkView, nextChunkViews ...*ChunkView) (chunkData []byte, err error) {
 
 	if c.lastChunkFileId == chunkView.FileId {
 		return c.lastChunkData, nil
diff --git a/weed/filer/stream.go b/weed/filer/stream.go
index dc6e414ca..d98229379 100644
--- a/weed/filer/stream.go
+++ b/weed/filer/stream.go
@@ -17,27 +17,32 @@ func StreamContent(masterClient *wdclient.MasterClient, w io.Writer, chunks []*f
 	// fmt.Printf("start to stream content for chunks: %+v\n", chunks)
 	chunkViews := ViewFromChunks(masterClient.LookupFileId, chunks, offset, size)
 
-	fileId2Url := make(map[string]string)
+	fileId2Url := make(map[string][]string)
 
 	for _, chunkView := range chunkViews {
 
-		urlString, err := masterClient.LookupFileId(chunkView.FileId)
+		urlStrings, err := masterClient.LookupFileId(chunkView.FileId)
 		if err != nil {
 			glog.V(1).Infof("operation LookupFileId %s failed, err: %v", chunkView.FileId, err)
 			return err
 		}
-		fileId2Url[chunkView.FileId] = urlString
+		fileId2Url[chunkView.FileId] = urlStrings
 	}
 
 	for _, chunkView := range chunkViews {
 
-		urlString := fileId2Url[chunkView.FileId]
-		err := util.ReadUrlAsStream(urlString, chunkView.CipherKey, chunkView.IsGzipped, chunkView.IsFullChunk(), chunkView.Offset, int(chunkView.Size), func(data []byte) {
-			w.Write(data)
-		})
-		if err != nil {
-			glog.V(1).Infof("read %s failed, err: %v", chunkView.FileId, err)
-			return err
+		urlStrings := fileId2Url[chunkView.FileId]
+		for _, urlString := range urlStrings {
+			err := util.ReadUrlAsStream(urlString, chunkView.CipherKey, chunkView.IsGzipped, chunkView.IsFullChunk(), chunkView.Offset, int(chunkView.Size), func(data []byte) {
+				w.Write(data)
+			})
+			if err != nil {
+				// data already written to w would be wrong
+				// but usually there are nothing written if fails to read
+				glog.V(1).Infof("read %s failed, err: %v", chunkView.FileId, err)
+			} else {
+				break
+			}
 		}
 	}
 
@@ -51,24 +56,28 @@ func ReadAll(masterClient *wdclient.MasterClient, chunks []*filer_pb.FileChunk)
 
 	buffer := bytes.Buffer{}
 
-	lookupFileIdFn := func(fileId string) (targetUrl string, err error) {
+	lookupFileIdFn := func(fileId string) (targetUrls []string, err error) {
 		return masterClient.LookupFileId(fileId)
 	}
 
 	chunkViews := ViewFromChunks(lookupFileIdFn, chunks, 0, math.MaxInt64)
 
 	for _, chunkView := range chunkViews {
-		urlString, err := lookupFileIdFn(chunkView.FileId)
+		urlStrings, err := lookupFileIdFn(chunkView.FileId)
 		if err != nil {
 			glog.V(1).Infof("operation LookupFileId %s failed, err: %v", chunkView.FileId, err)
 			return nil, err
 		}
-		err = util.ReadUrlAsStream(urlString, chunkView.CipherKey, chunkView.IsGzipped, chunkView.IsFullChunk(), chunkView.Offset, int(chunkView.Size), func(data []byte) {
-			buffer.Write(data)
-		})
-		if err != nil {
-			glog.V(1).Infof("read %s failed, err: %v", chunkView.FileId, err)
-			return nil, err
+		for _, urlString := range urlStrings {
+			err = util.ReadUrlAsStream(urlString, chunkView.CipherKey, chunkView.IsGzipped, chunkView.IsFullChunk(), chunkView.Offset, int(chunkView.Size), func(data []byte) {
+				buffer.Write(data)
+			})
+			if err != nil {
+				glog.V(1).Infof("read %s failed, err: %v", chunkView.FileId, err)
+				buffer.Reset()
+			} else {
+				break
+			}
 		}
 	}
 	return buffer.Bytes(), nil
@@ -89,7 +98,7 @@ var _ = io.ReadSeeker(&ChunkStreamReader{})
 
 func NewChunkStreamReaderFromFiler(masterClient *wdclient.MasterClient, chunks []*filer_pb.FileChunk) *ChunkStreamReader {
 
-	lookupFileIdFn := func(fileId string) (targetUrl string, err error) {
+	lookupFileIdFn := func(fileId string) (targetUrl []string, err error) {
 		return masterClient.LookupFileId(fileId)
 	}
 
@@ -169,17 +178,24 @@ func (c *ChunkStreamReader) Seek(offset int64, whence int) (int64, error) {
 }
 
 func (c *ChunkStreamReader) fetchChunkToBuffer(chunkView *ChunkView) error {
-	urlString, err := c.lookupFileId(chunkView.FileId)
+	urlStrings, err := c.lookupFileId(chunkView.FileId)
 	if err != nil {
 		glog.V(1).Infof("operation LookupFileId %s failed, err: %v", chunkView.FileId, err)
 		return err
 	}
 	var buffer bytes.Buffer
-	err = util.ReadUrlAsStream(urlString, chunkView.CipherKey, chunkView.IsGzipped, chunkView.IsFullChunk(), chunkView.Offset, int(chunkView.Size), func(data []byte) {
-		buffer.Write(data)
-	})
+	for _, urlString := range urlStrings {
+		err = util.ReadUrlAsStream(urlString, chunkView.CipherKey, chunkView.IsGzipped, chunkView.IsFullChunk(), chunkView.Offset, int(chunkView.Size), func(data []byte) {
+			buffer.Write(data)
+		})
+		if err != nil {
+			glog.V(1).Infof("read %s failed, err: %v", chunkView.FileId, err)
+			buffer.Reset()
+		} else {
+			break
+		}
+	}
 	if err != nil {
-		glog.V(1).Infof("read %s failed, err: %v", chunkView.FileId, err)
 		return err
 	}
 	c.buffer = buffer.Bytes()
diff --git a/weed/replication/repl_util/replication_utli.go b/weed/replication/repl_util/replication_utli.go
new file mode 100644
index 000000000..9b18275b5
--- /dev/null
+++ b/weed/replication/repl_util/replication_utli.go
@@ -0,0 +1,40 @@
+package repl_util
+
+import (
+	"github.com/chrislusf/seaweedfs/weed/filer"
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/replication/source"
+	"github.com/chrislusf/seaweedfs/weed/util"
+)
+
+func CopyFromChunkViews(chunkViews []*filer.ChunkView, filerSource *source.FilerSource, writeFunc func(data []byte) error) error {
+
+	for _, chunk := range chunkViews {
+
+		fileUrls, err := filerSource.LookupFileId(chunk.FileId)
+		if err != nil {
+			return err
+		}
+
+		var writeErr error
+
+		for _, fileUrl := range fileUrls {
+			err = util.ReadUrlAsStream(fileUrl+"?readDeleted=true", nil, false, chunk.IsFullChunk(), chunk.Offset, int(chunk.Size), func(data []byte) {
+				writeErr = writeFunc(data)
+			})
+			if err != nil {
+				glog.V(1).Infof("read from %s: %v", fileUrl, err)
+			} else if writeErr != nil {
+				glog.V(1).Infof("copy from %s: %v", fileUrl, writeErr)
+			} else {
+				break
+			}
+		}
+
+		if err != nil {
+			return err
+		}
+
+	}
+	return nil
+}
diff --git a/weed/replication/sink/azuresink/azure_sink.go b/weed/replication/sink/azuresink/azure_sink.go
index dab5cf4f4..df70be64b 100644
--- a/weed/replication/sink/azuresink/azure_sink.go
+++ b/weed/replication/sink/azuresink/azure_sink.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"github.com/chrislusf/seaweedfs/weed/replication/repl_util"
 	"net/url"
 	"strings"
 
@@ -107,25 +108,13 @@ func (g *AzureSink) CreateEntry(key string, entry *filer_pb.Entry, signatures []
 		return err
 	}
 
-	for _, chunk := range chunkViews {
-
-		fileUrl, err := g.filerSource.LookupFileId(chunk.FileId)
-		if err != nil {
-			return err
-		}
-
-		var writeErr error
-		readErr := util.ReadUrlAsStream(fileUrl+"?readDeleted=true", nil, false, chunk.IsFullChunk(), chunk.Offset, int(chunk.Size), func(data []byte) {
-			_, writeErr = appendBlobURL.AppendBlock(context.Background(), bytes.NewReader(data), azblob.AppendBlobAccessConditions{}, nil)
-		})
-
-		if readErr != nil {
-			return readErr
-		}
-		if writeErr != nil {
-			return writeErr
-		}
+	writeFunc := func(data []byte) error {
+		_, writeErr := appendBlobURL.AppendBlock(context.Background(), bytes.NewReader(data), azblob.AppendBlobAccessConditions{}, nil)
+		return writeErr
+	}
 
+	if err := repl_util.CopyFromChunkViews(chunkViews, g.filerSource, writeFunc); err != nil {
+		return err
 	}
 
 	return nil
diff --git a/weed/replication/sink/b2sink/b2_sink.go b/weed/replication/sink/b2sink/b2_sink.go
index cf212f129..24f0ecbbc 100644
--- a/weed/replication/sink/b2sink/b2_sink.go
+++ b/weed/replication/sink/b2sink/b2_sink.go
@@ -2,6 +2,7 @@ package B2Sink
 
 import (
 	"context"
+	"github.com/chrislusf/seaweedfs/weed/replication/repl_util"
 	"strings"
 
 	"github.com/chrislusf/seaweedfs/weed/filer"
@@ -95,31 +96,18 @@ func (g *B2Sink) CreateEntry(key string, entry *filer_pb.Entry, signatures []int
 	targetObject := bucket.Object(key)
 	writer := targetObject.NewWriter(context.Background())
 
-	for _, chunk := range chunkViews {
-
-		fileUrl, err := g.filerSource.LookupFileId(chunk.FileId)
-		if err != nil {
-			return err
-		}
-
-		var writeErr error
-		readErr := util.ReadUrlAsStream(fileUrl+"?readDeleted=true", nil, false, chunk.IsFullChunk(), chunk.Offset, int(chunk.Size), func(data []byte) {
-			_, err := writer.Write(data)
-			if err != nil {
-				writeErr = err
-			}
-		})
+	writeFunc := func(data []byte) error {
+		_, writeErr := writer.Write(data)
+		return writeErr
+	}
 
-		if readErr != nil {
-			return readErr
-		}
-		if writeErr != nil {
-			return writeErr
-		}
+	defer writer.Close()
 
+	if err := repl_util.CopyFromChunkViews(chunkViews, g.filerSource, writeFunc); err != nil {
+		return err
 	}
 
-	return writer.Close()
+	return nil
 
 }
 
diff --git a/weed/replication/sink/gcssink/gcs_sink.go b/weed/replication/sink/gcssink/gcs_sink.go
index c6bfa212a..badabc32c 100644
--- a/weed/replication/sink/gcssink/gcs_sink.go
+++ b/weed/replication/sink/gcssink/gcs_sink.go
@@ -3,6 +3,7 @@ package gcssink
 import (
 	"context"
 	"fmt"
+	"github.com/chrislusf/seaweedfs/weed/replication/repl_util"
 	"os"
 
 	"cloud.google.com/go/storage"
@@ -93,25 +94,14 @@ func (g *GcsSink) CreateEntry(key string, entry *filer_pb.Entry, signatures []in
 	chunkViews := filer.ViewFromChunks(g.filerSource.LookupFileId, entry.Chunks, 0, int64(totalSize))
 
 	wc := g.client.Bucket(g.bucket).Object(key).NewWriter(context.Background())
+	defer wc.Close()
 
-	for _, chunk := range chunkViews {
-
-		fileUrl, err := g.filerSource.LookupFileId(chunk.FileId)
-		if err != nil {
-			return err
-		}
-
-		err = util.ReadUrlAsStream(fileUrl+"?readDeleted=true", nil, false, chunk.IsFullChunk(), chunk.Offset, int(chunk.Size), func(data []byte) {
-			wc.Write(data)
-		})
-
-		if err != nil {
-			return err
-		}
-
+	writeFunc := func(data []byte) error {
+		_, writeErr := wc.Write(data)
+		return writeErr
 	}
 
-	if err := wc.Close(); err != nil {
+	if err := repl_util.CopyFromChunkViews(chunkViews, g.filerSource, writeFunc); err != nil {
 		return err
 	}
 
diff --git a/weed/replication/sink/s3sink/s3_write.go b/weed/replication/sink/s3sink/s3_write.go
index 8a8e7a92b..45265d1ba 100644
--- a/weed/replication/sink/s3sink/s3_write.go
+++ b/weed/replication/sink/s3sink/s3_write.go
@@ -157,11 +157,18 @@ func (s3sink *S3Sink) uploadPartCopy(key, uploadId string, partId int64, copySou
 }
 
 func (s3sink *S3Sink) buildReadSeeker(chunk *filer.ChunkView) (io.ReadSeeker, error) {
-	fileUrl, err := s3sink.filerSource.LookupFileId(chunk.FileId)
+	fileUrls, err := s3sink.filerSource.LookupFileId(chunk.FileId)
 	if err != nil {
 		return nil, err
 	}
 	buf := make([]byte, chunk.Size)
-	util.ReadUrl(fileUrl, nil, false, false, chunk.Offset, int(chunk.Size), buf)
+	for _, fileUrl := range fileUrls {
+		_, err = util.ReadUrl(fileUrl, nil, false, false, chunk.Offset, int(chunk.Size), buf)
+		if err != nil {
+			glog.V(1).Infof("read from %s: %v", fileUrl, err)
+		} else {
+			break
+		}
+	}
 	return bytes.NewReader(buf), nil
 }
diff --git a/weed/replication/source/filer_source.go b/weed/replication/source/filer_source.go
index 9106ee98b..c3ef8835c 100644
--- a/weed/replication/source/filer_source.go
+++ b/weed/replication/source/filer_source.go
@@ -41,7 +41,7 @@ func (fs *FilerSource) DoInitialize(grpcAddress string, dir string) (err error)
 	return nil
 }
 
-func (fs *FilerSource) LookupFileId(part string) (fileUrl string, err error) {
+func (fs *FilerSource) LookupFileId(part string) (fileUrls []string, err error) {
 
 	vid2Locations := make(map[string]*filer_pb.Locations)
 
@@ -64,29 +64,38 @@ func (fs *FilerSource) LookupFileId(part string) (fileUrl string, err error) {
 
 	if err != nil {
 		glog.V(1).Infof("LookupFileId volume id %s: %v", vid, err)
-		return "", fmt.Errorf("LookupFileId volume id %s: %v", vid, err)
+		return nil, fmt.Errorf("LookupFileId volume id %s: %v", vid, err)
 	}
 
 	locations := vid2Locations[vid]
 
 	if locations == nil || len(locations.Locations) == 0 {
 		glog.V(1).Infof("LookupFileId locate volume id %s: %v", vid, err)
-		return "", fmt.Errorf("LookupFileId locate volume id %s: %v", vid, err)
+		return nil, fmt.Errorf("LookupFileId locate volume id %s: %v", vid, err)
 	}
 
-	fileUrl = fmt.Sprintf("http://%s/%s", locations.Locations[0].Url, part)
+	for _, loc := range locations.Locations {
+		fileUrls = append(fileUrls, fmt.Sprintf("http://%s/%s", loc.Url, part))
+	}
 
 	return
 }
 
 func (fs *FilerSource) ReadPart(part string) (filename string, header http.Header, resp *http.Response, err error) {
 
-	fileUrl, err := fs.LookupFileId(part)
+	fileUrls, err := fs.LookupFileId(part)
 	if err != nil {
 		return "", nil, nil, err
 	}
 
-	filename, header, resp, err = util.DownloadFile(fileUrl)
+	for _, fileUrl := range fileUrls {
+		filename, header, resp, err = util.DownloadFile(fileUrl)
+		if err != nil {
+			glog.V(1).Infof("fail to read from %s: %v", fileUrl, err)
+		} else {
+			break
+		}
+	}
 
 	return filename, header, resp, err
 }
diff --git a/weed/server/filer_grpc_server.go b/weed/server/filer_grpc_server.go
index ecd23413f..5166f0896 100644
--- a/weed/server/filer_grpc_server.go
+++ b/weed/server/filer_grpc_server.go
@@ -135,16 +135,19 @@ func (fs *FilerServer) LookupVolume(ctx context.Context, req *filer_pb.LookupVol
 	return resp, nil
 }
 
-func (fs *FilerServer) lookupFileId(fileId string) (targetUrl string, err error) {
+func (fs *FilerServer) lookupFileId(fileId string) (targetUrls []string, err error) {
 	fid, err := needle.ParseFileIdFromString(fileId)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 	locations, found := fs.filer.MasterClient.GetLocations(uint32(fid.VolumeId))
 	if !found || len(locations) == 0 {
-		return "", fmt.Errorf("not found volume %d in %s", fid.VolumeId, fileId)
+		return nil, fmt.Errorf("not found volume %d in %s", fid.VolumeId, fileId)
+	}
+	for _, loc := range locations {
+		targetUrls = append(targetUrls, fmt.Sprintf("http://%s/%s", loc.Url, fileId))
 	}
-	return fmt.Sprintf("http://%s/%s", locations[0].Url, fileId), nil
+	return
 }
 
 func (fs *FilerServer) CreateEntry(ctx context.Context, req *filer_pb.CreateEntryRequest) (resp *filer_pb.CreateEntryResponse, err error) {
diff --git a/weed/wdclient/vid_map.go b/weed/wdclient/vid_map.go
index 97df49cb6..cee2da6e1 100644
--- a/weed/wdclient/vid_map.go
+++ b/weed/wdclient/vid_map.go
@@ -44,38 +44,36 @@ func (vc *vidMap) getLocationIndex(length int) (int, error) {
 	return int(atomic.AddInt32(&vc.cursor, 1)) % length, nil
 }
 
-func (vc *vidMap) LookupVolumeServerUrl(vid string) (serverUrl string, err error) {
+func (vc *vidMap) LookupVolumeServerUrl(vid string) (serverUrls []string, err error) {
 	id, err := strconv.Atoi(vid)
 	if err != nil {
 		glog.V(1).Infof("Unknown volume id %s", vid)
-		return "", err
+		return nil, err
 	}
 
-	return vc.GetRandomLocation(uint32(id))
-}
-
-func (vc *vidMap) LookupFileId(fileId string) (fullUrl string, err error) {
-	parts := strings.Split(fileId, ",")
-	if len(parts) != 2 {
-		return "", errors.New("Invalid fileId " + fileId)
+	locations, found := vc.GetLocations(uint32(id))
+	if !found {
+		return nil, fmt.Errorf("volume %d not found", id)
 	}
-	serverUrl, lookupError := vc.LookupVolumeServerUrl(parts[0])
-	if lookupError != nil {
-		return "", lookupError
+	for _, loc := range locations {
+		serverUrls = append(serverUrls, loc.Url)
 	}
-	return "http://" + serverUrl + "/" + fileId, nil
+	return
 }
 
-func (vc *vidMap) LookupVolumeServer(fileId string) (volumeServer string, err error) {
+func (vc *vidMap) LookupFileId(fileId string) (fullUrls []string, err error) {
 	parts := strings.Split(fileId, ",")
 	if len(parts) != 2 {
-		return "", errors.New("Invalid fileId " + fileId)
+		return nil, errors.New("Invalid fileId " + fileId)
 	}
-	serverUrl, lookupError := vc.LookupVolumeServerUrl(parts[0])
+	serverUrls, lookupError := vc.LookupVolumeServerUrl(parts[0])
 	if lookupError != nil {
-		return "", lookupError
+		return nil, lookupError
 	}
-	return serverUrl, nil
+	for _, serverUrl := range serverUrls {
+		fullUrls = append(fullUrls, "http://"+serverUrl+"/"+fileId)
+	}
+	return
 }
 
 func (vc *vidMap) GetVidLocations(vid string) (locations []Location, err error) {
@@ -99,23 +97,6 @@ func (vc *vidMap) GetLocations(vid uint32) (locations []Location, found bool) {
 	return
 }
 
-func (vc *vidMap) GetRandomLocation(vid uint32) (serverUrl string, err error) {
-	vc.RLock()
-	defer vc.RUnlock()
-
-	locations := vc.vid2Locations[vid]
-	if len(locations) == 0 {
-		return "", fmt.Errorf("volume %d not found", vid)
-	}
-
-	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) {
 	vc.Lock()
 	defer vc.Unlock()