private List<BlockDeviceMapping> getNewEphemeralDeviceMapping() { final List<BlockDeviceMapping> oldDeviceMapping = getAmiBlockDeviceMappings(); final Set<String> occupiedDevices = new HashSet<String>(); for (final BlockDeviceMapping mapping : oldDeviceMapping) { occupiedDevices.add(mapping.getDeviceName()); } final List<String> available = new ArrayList<String>( Arrays.asList("ephemeral0", "ephemeral1", "ephemeral2", "ephemeral3")); final List<BlockDeviceMapping> newDeviceMapping = new ArrayList<BlockDeviceMapping>(4); for (char suffix = 'b'; suffix <= 'z' && !available.isEmpty(); suffix++) { final String deviceName = String.format("/dev/xvd%s", suffix); if (occupiedDevices.contains(deviceName)) continue; final BlockDeviceMapping newMapping = new BlockDeviceMapping().withDeviceName(deviceName).withVirtualName(available.get(0)); newDeviceMapping.add(newMapping); available.remove(0); } return newDeviceMapping; }