I'm considering to replace my optical drive in my MacBook Pro with an SSD. When using it as separate Volume, the advantage is that you can spin down the HDD, thus reduce noise and first and foremost, battery consumption. Manually managing the files however is a nightmare IMO.
Setting up a Fusion Drive solves this problem, however it seems that the HDD is constantly spinning whenever you access the Fusion Drive, regardless wether the data sits actually on the SSD portion or the HDD. See here (the mentioned ArsTechnica test was done on a Mac mini, question is whether the Fusion Drive managing behaves any different on portable Macs with different Power Management settings).
Question: Is there any way to force the FusionDrive manager (coreStorage?) to spin down the HDD, when the data comes off the SSD and the HDD has nothing to do?