-C flag will display a progress bar. Performance differences depending on how fsck is called.
And very cool, if
e2fsck is already running, you can send a
USR1 signal for it to start displaying a progress bar.
USR2 to stop. Example:
killall -USR1 e2fsck
-C Display completion/progress bars for those filesys-
tems checkers (currently only for ext2) which sup-
port them. Fsck will manage the filesystem check-
ers so that only one of them will display a
progress bar at a time.
-C fd This option causes e2fsck to write completion
information to the specified file descriptor so
that the progress of the filesystem check can be
monitored. This option is typically used by pro-
grams which are running e2fsck. If the file
descriptor specified is 0, e2fsck will print a com-
pletion bar as it goes about its business. This
requires that e2fsck is running on a video console