MacBook SSD replacement — sudden motion shock sensor in optical bay? When looking to upgrade a MacBook Pro with a solid state drive (SSD), one option is to:


First, install the SSD instead of the spinning hard disk drive (HDD).
Then, install the HDD instead of the optical drive (SuperDrive).


At present, many websites (if not most) suggest to do it this way. However, I am concerned about the safety to the spinning HDD (hard disk drive) when in the SuperDrive slot.

The main bay has a sudden-motion-sensor (SMS). It is an accelerometer that detects when the MacBook is falling and prevents damage to the HDD as it is spinning by retracting the reader arm that could scratch the hard disk — damaging/corrupting data.

Although the SuperDrive bay may have the same SATA connector as the main bay (depends on the year of your machine, some have a combination of SATA II and III), it is suggested that it may not have an SMS, which can be a pretty serious issue:


  Why not install the SSD in the regular hard drive bay? Good idea! The
  only problem is that the regular hard drive bay is the only bay that
  features sudden motion protection. If you drop your MacBook, it’s
  smart enough to safely park your non-SSD hard drive so it won’t be
  damaged by the impact. The optical bay interface has no such feature.
  This is harmless to your ... SSD because it has no moving parts,
  but any spinning platter-based drive [HDD] will be at risk if installed in
  the optical bay. 
  
  You can have it both ways if your secondary hard drive has its own
  native sudden motion detection (the ... factory-installed MacBook hard
  drive [does not]).


But posts on a forum suggest otherwise.

Which do we believe?





If the optical bay lacks the shock sensor, then it would likely be better to leave the HDD where it is, and install the SSD in the optical bay, but this method seems to have an issue with waking from hibernation and sleep.
This solution may not directly answer your question, but it may be relevant: I would advise you against putting your HDD in the optical bay.

I tried that. Putting the SSD in place of the HDD, and moving the HDD in the optical bay, which is just under the keyboard… And I got to hear the noise of the HDD spinning and the noise the heads when accessing cylinders… Bad idea. After a few hours, I switched HDD and SSD.

So, I would recommend you to leave the HDD in its bay and to put the SSD in the optical bay. That way your question is solved, and you don't get to hear the HDD working.
And if you notice an extra delay when booting, just select the SSD (which is in the optical bay) as booting drive in the system preferences. You will need to enter your password twice, once and for all. Then, your mac will immediately find the SSD when starting up.