Oracle recommend to keep free space of 90 cm behind the machine.
Unfortunately we have only 60 cm free space behind the machine .
Questions : Does the 90 percent is mandatory ? Is there going to be problem to take out from the exadata machine a server in case of problem ?
With that amount of space, you'll barely be able to get the door open in the back, so it could be problematic. Also, the airflow goes from front to back, so you'll have less room for the hot air to dissipate in the back. How much space do you have in front of the machine? The owner's guide says that you need 152cm in front. That's critical, because the servers pull out from the front. If you have enough room in front of the machine, you could always move the rack forward to give ample space in the back.