drop big table freeze server
What exact version?

DELETE on a huge table will take a huge amount of time because it is building an "undo" log in case of a crash.  Don't use that technique.

What was the value of innodb_file_per_table when the table was built?


If OFF (or 0), the table is in ibdata1, which will not shrink and return space to the OS.  It will only free up blocks for subsequent use.
If ON (or 1), then DROP TABLE will be much faster, but still not instantaneous.
If you have FOREIGN KEYs connecting the table (in either direction), well, let's see them.  (SHOW CREATE TABLE)


If you need to delete a big part of a table, here are several techniques.  This discusses how to do the delete in chunks, and takes Replication issues into account.