There's a known issue that dm-cache doesn't handle table preload properly (see kernel commit 9b1cc9f251af), causing wrong cache statistics display and failure detection of metadata errors. Since that dm-cache hasn't yet implement the read-only mode (ie., we cannot open the cache target read-only as there's no read_only feature in the table), we must have to handle the preload issue with care, or we'll end up with an unresumable device when there's metadata error.