adding volume type

weed/storage/volume_info.go

@@ -14,6 +14,7 @@ type VolumeInfo struct {
 	Size              uint64
 	ReplicaPlacement  *super_block.ReplicaPlacement
 	Ttl               *needle.TTL
+	VolumeType        VolumeType
 	Collection        string
 	Version           needle.Version
 	FileCount         int

weed/storage/volume_type.go

@@ -0,0 +1,23 @@
+package storage
+
+import "fmt"
+
+type VolumeType string
+
+const (
+	HardDriveType VolumeType = ""
+	SsdType                  = "ssd"
+)
+
+func ToVolumeType(vt string) (volumeType VolumeType, err error) {
+	volumeType = HardDriveType
+	switch vt {
+	case "", "hdd":
+		volumeType = HardDriveType
+	case "ssd":
+		volumeType = SsdType
+	default:
+		err = fmt.Errorf("parse VolumeType %s: expecting hdd or ssd\n", vt)
+	}
+	return
+}