Another option is to shrink the file system from 4 devices to 3 by deleting one. This assumes there's sufficient room for the data to exist on 3 devices. At least this way the volume is never degraded. You could do a balance after adding the new 4th device, but that's optional. Since it's empty, all new writes will have an a copy always going to the new 4th device and then the b copy to one of the other three. Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
