nofail does not permit the boot sequence to continue if the drive fails to mount.
This is what
fstab(5) says about
The mountall(8) program that mounts filesystem during boot also recog‐
nises additional options that the ordinary mount(8) tool does not.
bootwait which can be applied to remote filesystems
mounted outside of /usr or /var, without which mountall(8) would not
hold up the boot for these;
nobootwait which can be applied to
non-remote filesystems to explicitly instruct mountall(8) not to hold up
the boot for them;
optional which causes the entry to be ignored if
the filesystem type is not known at boot time; and
which permits a mountpoint to be mounted before its parent mountpoint
(this latter should be used carefully, as it can cause boot hangs).
fstab(5) has this to say about
nofail do not report errors for this device if it does not