uninterruptible sleep (state D)

The D in ps's STAT column: the process is inside a system call the kernel will not interrupt, and that call is nearly always waiting on storage. Signals do arrive — they are recorded as pending and delivered when the call returns. If the failing disk or the vanished network mount never answers, the call never returns, and neither does the signal. This is what a process that "ignores" three kills and then a kill -9 actually is. It is not stubbornness: no signal, SIGKILL included, gets a D process off that call. A ps -o pid,stat,comm -p 1841 showing D tar tells you to stop signalling and go look at the storage — dmesg, the mount, the disk. The lever is the storage, never the signal.