add tool to change a volume's replication

fix https://github.com/chrislusf/seaweedfs/issues/29

unmaintained/change_replication/change_replication.go

@@ -0,0 +1,84 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"path"
+	"strconv"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/storage"
+)
+
+var (
+	fixVolumePath       = flag.String("dir", "/tmp", "data directory to store files")
+	fixVolumeCollection = flag.String("collection", "", "the volume collection name")
+	fixVolumeId         = flag.Int("volumeId", -1, "a volume id. The volume should already exist in the dir. The volume index file should not exist.")
+	targetReplica       = flag.String("replication", "", "If just empty, only print out current replication setting.")
+)
+
+/*
+This is to change replication factor in .dat file header. Need to shut down the volume servers
+that has those volumes.
+
+1. fix the .dat file in place
+	// just see the replication setting
+	go run change_replication.go -volumeId=9 -dir=/Users/chrislu/Downloads
+		Current Volume Replication: 000
+	// fix the replication setting
+	go run change_replication.go -volumeId=9 -dir=/Users/chrislu/Downloads -replication 001
+		Current Volume Replication: 000
+		Changing to: 001
+		Done.
+
+2. copy the fixed .dat and related .idx files to some remote server
+3. restart volume servers or start new volume servers.
+*/
+func main() {
+	flag.Parse()
+	fileName := strconv.Itoa(*fixVolumeId)
+	if *fixVolumeCollection != "" {
+		fileName = *fixVolumeCollection + "_" + fileName
+	}
+	datFile, err := os.OpenFile(path.Join(*fixVolumePath, fileName+".dat"), os.O_RDWR, 0644)
+	if err != nil {
+		glog.Fatalf("Open Volume Data File [ERROR]: %v", err)
+	}
+	defer datFile.Close()
+
+	header := make([]byte, storage.SuperBlockSize)
+	if _, e := datFile.Read(header); e != nil {
+		glog.Fatalf("cannot read volume %s super block: %v", fileName+".dat", e)
+	}
+	superBlock, err := storage.ParseSuperBlock(header)
+
+	if err != nil {
+		glog.Fatalf("cannot parse existing super block: %v", err)
+	}
+
+	fmt.Printf("Current Volume Replication: %s\n", superBlock.ReplicaPlacement)
+
+	if *targetReplica == "" {
+		return
+	}
+
+	replica, err := storage.NewReplicaPlacementFromString(*targetReplica)
+
+	if err != nil {
+		glog.Fatalf("cannot parse target replica %s: %v", *targetReplica, err)
+	}
+
+	fmt.Printf("Changing to: %s\n", replica)
+
+	superBlock.ReplicaPlacement = replica
+
+	header = superBlock.Bytes()
+
+	if n, e := datFile.WriteAt(header, 0); n == 0 || e != nil {
+		glog.Fatalf("cannot write super block: %v", e)
+	}
+
+	fmt.Println("Done.")
+
+}