So what exactly does a Momentus XT do in the optibay

Discussion in 'MacBook Pro' started by nudoru, Jan 25, 2013.

  1. nudoru macrumors regular

    Feb 27, 2012
    My Google-fu isn't turning up specifics on this issue - just people saying there are "issues."

    So I'll just post my question - I've got a late 2011 MBP and with a Momentus XT 750 running perfectly as the main hard drive. I've got a 640 WD Blue in the optibay running perfectly also. I've just ordered an SSD (NewEgg has the Samsung 840 PRO for $199 today!) and would like to put the quicker Momentus in the optibay. And it has my existing BootCamp partition on it as well.

    What problems may I encounter with this? From what I've read that MPBs older (than mine?) do not support SATA 6 in the optibay, but I figure the drive will negotiate down to 3 and be just fine. I can confirm that the negotiated speed of the WD there now is 3 and the link speed is 6.

    I'd just do it and try, but putting a drive in the optibay is such a PITA, I'd like to hear from experience before I learn the hardway.

  2. alphaod macrumors Core


    Feb 9, 2008
    Putting the hybrid drive in the optibay will be just like putting the hybrid drive in the main bay. If you do not use it as a boot drive, it will still put your most commonly used files into the flash memory.
  3. nudoru thread starter macrumors regular

    Feb 27, 2012
    Thanks ... figured that part would work - it's just with people saying there are problems with it. Just interested in what that meant.
  4. NewishMacGuy macrumors 6502a


    Aug 2, 2007
    What they likely mean is that because the MoXT is a SATA III drive, it won't work reliably in the optibay of a 2011 uMBP-15. The 2011 model had issues running SATA III drives in that spot (supposedly because of RF interference with the SATA controller cable). This is a well documented issue with any SATA III drive, not just the MoXT. The 2010 model will work fine with a SATA III drive in the optibay, but will max out at slightly less than 300MB/s speeds (which is more than enough for the MoXT), and the 2012 model will work fine and max out at speeds twice as high, but the 2011 model just won't work reliably.

    Some people have claimed that the MoXT won't work as part of a DIY Fusion drive because it's a hybrid, but this is an ill-informed view as the computer can't tell that it's a hybrid. To the computer, the MoXT looks like any other 7200rpm HDD, but with a MUCH bigger than normal cache.

    So, the answer to your original question is that the MoXT isn't going to work well in the optibay your computer. The fact that your current WD Blue is reporting a 3GB/s negotiated speed suggests that it's a SATA II drive, which is fine in the 2011 optibay, so you'll likely just have to stick with that.

  5. nudoru thread starter macrumors regular

    Feb 27, 2012
    Thanks for the explanation!

    I'm seeing that now ... just booted after switching the drives and, while the computer can see it and get sizing information, it can't read any data off of it. :p

    Switching back now ... i'm getting good at this.

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