@@ -500,21 +500,41 @@ func (devices *DeviceSet) incNextDeviceId() {

 	devices.NextDeviceId = (devices.NextDeviceId + 1) & MaxDeviceId

 }

-func (devices *DeviceSet) getNextDeviceId() int {

+func (devices *DeviceSet) getNextFreeDeviceId() (int, error) {

 	devices.incNextDeviceId()

-	return devices.NextDeviceId

+	for i := 0; i <= MaxDeviceId; i++ {

+		if devices.isDeviceIdFree(devices.NextDeviceId) {

+			devices.markDeviceIdUsed(devices.NextDeviceId)

+			return devices.NextDeviceId, nil

+		}

+		devices.incNextDeviceId()

+	}

+

+	return 0, fmt.Errorf("Unable to find a free device Id")

 }

 func (devices *DeviceSet) createRegisterDevice(hash string) (*DevInfo, error) {

-	deviceId := devices.getNextDeviceId()

+	deviceId, err := devices.getNextFreeDeviceId()

+	if err != nil {

+		return nil, err

+	}

+

 	for {

 		if err := devicemapper.CreateDevice(devices.getPoolDevName(), deviceId); err != nil {

 			if devicemapper.DeviceIdExists(err) {

-				// Device Id already exists. Try a new one.

-				deviceId = devices.getNextDeviceId()

+				// Device Id already exists. This should not

+				// happen. Now we have a mechianism to find

+				// a free device Id. So something is not right.

+				// Give a warning and continue.

+				log.Errorf("Warning: Device Id %d exists in pool but it is supposed to be unused", deviceId)

+				deviceId, err = devices.getNextFreeDeviceId()

+				if err != nil {

+					return nil, err

+				}

 				continue

 			}

 			log.Debugf("Error creating device: %s", err)

+			devices.markDeviceIdFree(deviceId)

 			return nil, err

 		}

 		break

@@ -525,27 +545,41 @@ func (devices *DeviceSet) createRegisterDevice(hash string) (*DevInfo, error) {

 	info, err := devices.registerDevice(deviceId, hash, devices.baseFsSize, transactionId)

 	if err != nil {

 		_ = devicemapper.DeleteDevice(devices.getPoolDevName(), deviceId)

+		devices.markDeviceIdFree(deviceId)

 		return nil, err

 	}

 	if err := devices.updatePoolTransactionId(); err != nil {

 		devices.unregisterDevice(deviceId, hash)

 		devicemapper.DeleteDevice(devices.getPoolDevName(), deviceId)

+		devices.markDeviceIdFree(deviceId)

 		return nil, err

 	}

 	return info, nil

 }

 func (devices *DeviceSet) createRegisterSnapDevice(hash string, baseInfo *DevInfo) error {

-	deviceId := devices.getNextDeviceId()

+	deviceId, err := devices.getNextFreeDeviceId()

+	if err != nil {

+		return err

+	}

+

 	for {

 		if err := devicemapper.CreateSnapDevice(devices.getPoolDevName(), deviceId, baseInfo.Name(), baseInfo.DeviceId); err != nil {

 			if devicemapper.DeviceIdExists(err) {

-				// Device Id already exists. Try a new one.

-				deviceId = devices.getNextDeviceId()

+				// Device Id already exists. This should not

+				// happen. Now we have a mechianism to find

+				// a free device Id. So something is not right.

+				// Give a warning and continue.

+				log.Errorf("Warning: Device Id %d exists in pool but it is supposed to be unused", deviceId)

+				deviceId, err = devices.getNextFreeDeviceId()

+				if err != nil {

+					return err

+				}

 				continue

 			}

 			log.Debugf("Error creating snap device: %s", err)

+			devices.markDeviceIdFree(deviceId)

 			return err

 		}

 		break

@@ -554,6 +588,7 @@ func (devices *DeviceSet) createRegisterSnapDevice(hash string, baseInfo *DevInf

 	transactionId := devices.allocateTransactionId()

 	if _, err := devices.registerDevice(deviceId, hash, baseInfo.Size, transactionId); err != nil {

 		devicemapper.DeleteDevice(devices.getPoolDevName(), deviceId)

+		devices.markDeviceIdFree(deviceId)

 		log.Debugf("Error registering device: %s", err)

 		return err

 	}

@@ -561,6 +596,7 @@ func (devices *DeviceSet) createRegisterSnapDevice(hash string, baseInfo *DevInf

 	if err := devices.updatePoolTransactionId(); err != nil {

 		devices.unregisterDevice(deviceId, hash)

 		devicemapper.DeleteDevice(devices.getPoolDevName(), deviceId)

+		devices.markDeviceIdFree(deviceId)

 		return err

 	}

 	return nil

@@ -966,6 +1002,8 @@ func (devices *DeviceSet) deleteDevice(info *DevInfo) error {

 		return err

 	}

+	devices.markDeviceIdFree(info.DeviceId)

+

 	return nil

 }