We have been testing InnoDB compression (T139055).
The results have been pretty good:
S1 - 1.3T -> 490G S3 - 500GB less ( only compressed the top3 tables - (revision, pagelinks, templatelinks) ) S4 - 1.3T -> 467G
We have seen no peformance drawbacks so far.
So when possible, try to keep compressing.
dbstore and lab servers are good candidates at the moment.
ALTER TABLE XXXXX row_format=compressed key_block_size=8;