func parseIkey(ik []byte) (ukey []byte, seq uint64, kt kType, err error) {
    if len(ik) < 8 {
        return nil, 0, 0, newErrIkeyCorrupted(ik, "invalid length")
    }
    num := binary.LittleEndian.Uint64(ik[len(ik)-8:])