Major:

change replication_type to ReplicaPlacement, hopefully cleaner code
works for 9 possible ReplicaPlacement
xyz
x : number of copies on other data centers
y : number of copies on other racks
z : number of copies on current rack
x y z each can be 0,1,2

Minor:
weed server "-mdir" default to "-dir" if empty

go/storage/replica_placement.go

@@ -0,0 +1,61 @@
+package storage
+
+import (
+	"errors"
+	"fmt"
+)
+
+const (
+	ReplicaPlacementCount = 9
+)
+
+type ReplicaPlacement struct {
+	SameRackCount       int
+	DiffRackCount       int
+	DiffDataCenterCount int
+}
+
+func NewReplicaPlacementFromString(t string) (*ReplicaPlacement, error) {
+	rp := &ReplicaPlacement{}
+	for i, c := range t {
+		count := int(c - '0')
+		if 0 <= count && count <= 2 {
+			switch i {
+			case 0:
+				rp.DiffDataCenterCount = count
+			case 1:
+				rp.DiffRackCount = count
+			case 2:
+				rp.SameRackCount = count
+			}
+		} else {
+			return rp, errors.New("Unknown Replication Type:" + t)
+		}
+	}
+	return rp, nil
+}
+
+func NewReplicaPlacementFromByte(b byte) (*ReplicaPlacement, error) {
+	return NewReplicaPlacementFromString(fmt.Sprintf("%d", b))
+}
+
+func (rp *ReplicaPlacement) Byte() byte {
+	ret := rp.DiffDataCenterCount*100 + rp.DiffRackCount*10 + rp.SameRackCount
+	return byte(ret)
+}
+
+func (rp *ReplicaPlacement) String() string {
+	b := make([]byte, 3)
+	b[0] = byte(rp.DiffDataCenterCount + '0')
+	b[1] = byte(rp.DiffRackCount + '0')
+	b[2] = byte(rp.SameRackCount + '0')
+	return string(b)
+}
+
+func (rp *ReplicaPlacement) GetCopyCount() int {
+	return rp.DiffDataCenterCount + rp.DiffRackCount + rp.SameRackCount + 1
+}
+
+func (rp *ReplicaPlacement) GetReplicationLevelIndex() int {
+	return rp.DiffDataCenterCount*3 + rp.DiffRackCount*3 + rp.SameRackCount
+}