toughen weedfs clustering, adding synchronizing max volume id among

peers in order to avoid the same volume id being assigned twice
1. moving raft.Server to topology
2. adding max volume id command for raft

go/topology/cluster_commands.go

@@ -0,0 +1,31 @@
+package topology
+
+import (
+	"code.google.com/p/weed-fs/go/glog"
+	"code.google.com/p/weed-fs/go/storage"
+	"github.com/goraft/raft"
+)
+
+type MaxVolumeIdCommand struct {
+	MaxVolumeId storage.VolumeId `json:"maxVolumeId"`
+}
+
+func NewMaxVolumeIdCommand(value storage.VolumeId) *MaxVolumeIdCommand {
+	return &MaxVolumeIdCommand{
+		MaxVolumeId: value,
+	}
+}
+
+func (c *MaxVolumeIdCommand) CommandName() string {
+	return "MaxVolumeId"
+}
+
+func (c *MaxVolumeIdCommand) Apply(server raft.Server) (interface{}, error) {
+	topo := server.Context().(*Topology)
+	before := topo.GetMaxVolumeId()
+	topo.UpAdjustMaxVolumeId(c.MaxVolumeId)
+
+	glog.V(0).Infoln("max volume id", before, "==>", topo.GetMaxVolumeId())
+
+	return nil, nil
+}