ever since I began sharing files between Linux and Windows systems I've
been suffering from one major problem that affects smb, nfs as well as
cifs: Long lock ups on server down times.
If the serving computer shuts down / crashes, every process hangs when
trying to access the still mounted share. Just try df, mount or ls. You
can't even umount the share in this condition! When using smb this was
very severe as you couldn't mount a share with a "soft" option. So the
process in fact just hung until I pressed reset. Now, with cifs it is
much better. But still the timeout is very long. And you still cannot
umount an offline share to prevent further lock ups.
Now my suggestion would be to make the timeout adjustable (now it is
something like 30 seconds on every access). And maybe automatic umounts
if a share isn't available anymore. At least one should be able to
umount such a share.