MBP Motion Sensor for SSD

Discussion in 'MacBook Pro' started by fuzzylemurs, Apr 28, 2010.

  1. fuzzylemurs macrumors member

    Jul 10, 2008
    I have ordered several new MBPs (5 with SSDs...) for my clients, but have a mechanical HDD for myself in my new MBP; I just thought about the motion sensor that locks mechanical HDD read heads on sudden acceleration, and realized that it is an OS feature... Has anyone that has a mid 2010 MBP and a SSD noticed HDD lock in sudden movement with a SSD?

    You can simulate this 'lock' by moving the MacBook suddenly when playing content from the drive... Has anyone seen the drive cause playback to halt for 2-3 seconds while the SSD 'recovers'? If so, this needs to be fixed...
  2. shadowness macrumors regular

    Apr 24, 2010
    not applicable for SSD's

    The SMS (Sudden motion sensor) feature is not applicable for SSD's as there are no moving parts in an SSD.

    The feature works great in HDD's and when the SMS registers a sudden movement it parks the HDD r/w heads so there is no Disk head crash which causes data loss.

    SSD's are flas based and thus do not require SMS.

    But if you go the Optibay route and install an SSD & HDD, SMS will function normally but only on the HDD.:eek:

    Hope this helps !!! :D
  3. fuzzylemurs thread starter macrumors member

    Jul 10, 2008
    Yes, I know the logic behind the SMS, but I want to know if OS 10.6+ knows to disable the SMS if it senses a SSD in place.. are you telling me definitively that it does?
  4. Chundles macrumors G4


    Jul 4, 2005
    Um, I'm not sure if you're serious but here's how it works. The SMS tells the HDD to park the heads if there's a sudden change in the laptop's acceleration.

    There are no heads in an SSD so nothing happens. There are no moving parts in an SSD so nothing happens. It doesn't stop data coming through because there are no moving parts to stop.
  5. fuzzylemurs thread starter macrumors member

    Jul 10, 2008
    I am serious, and I understand what you are saying... But I have read that in previous MBP releases that the SMS actually stops the I/O from the controller, which could cause data restriction...

    I guess what I am asking, is that a SSD user play a decent video file off the drive, and shakes their laptop!

    Does it skip?

    Am I really the only one wondering this?
  6. Eddyisgreat macrumors 601

    Oct 24, 2007
    lol lot of off topic theorhetical "meaning of life" type answers today ;)

    Does the SSD ignore any attempts from the OS to park the heads? Maybe. I don't have time to do such in depth research.

    If you want to enable/disable it use the following command(s):
    Disable: sudo pmset -a sms 0
    Enable: sudo pmset -a sms 1
  7. shadowness macrumors regular

    Apr 24, 2010
    just about to post that!!!
    safe bet. Just disable SMS on all systems using SSD's
  8. fuzzylemurs thread starter macrumors member

    Jul 10, 2008
    I am hate to be an ass, or seem redundant, but here goes...

    Are you fellas saying that if we have an SSD that we should do as stated above; or are you saying that it would be a redundancy?

    I only want to know for myself, or our readers, if Mac OS 10.6+ automatically disables SMS...

    If it does not, do you think it be acceptable for the general public to just 'know' they have to run a command to disable sms?
  9. shadowness macrumors regular

    Apr 24, 2010
    as far as i know its not a requirement to disable SMS if you are using SSD.

    SMS just sends the signal to the HDD to park the heads. its doesnt do anything on the I/O controllers or anything. Obviously any ongoing data I/O operation is going to be paused or stopped which IMHO is better than having your HDD head or Platter getting damaged!!!

    on SSD's even if SMS sends a signal it just going to ignored as there are no heads to park.
  10. Eddyisgreat macrumors 601

    Oct 24, 2007
    Shadowness: Do you have any reports of this? Just curious. Back in the day when SSDs were bleeding edge and we were trying them out on these boards, many people said they experienced hangs whenever they moved the system because of SMS.

    fuzzylemurs: I hear what you are saying but you have to remember.
    1. There's no evidence (that I can find) that suggests OS X does any type of verification for an SSD using vendor strings or anything like that so, no, SMS isn't automatically disabled.
    2. There's no evidence that Apple hasn't made provisions for it's own (Samsung?) based SSD. They may very well detect and disable it through the OS for their own, since it really is the only Apple "sanctioned" SSD.

    Though a small group overall, lots of us use the intel x25-m so we had to deal with alot of this stuff on our own, so the average joe wouldn't drop 200 bucks on an 80 gig drive unless their tech buddy told them to, and then the tech guy has probably been around enough to disable SMS. This is why for non power users who want SSD computing without the hassle will just opt for the factory upgrade.
  11. shadowness macrumors regular

    Apr 24, 2010
    I am sorry and i stand corrected if this is true.... that Disabling SMS for SSD only MBP is better.

    but for MBP's with SSD + HDD leave SMS as it is

    read the full post here http://forum.notebookreview.com/apple-mac-os-x/479350-ssd-optibay-install-mid-2010-15-unibody.html
  12. sascha h-k macrumors 6502

    sascha h-k

    Apr 26, 2004
    vienna / austria
    disable sms for ssd is a MUST and also no sleep for "hdd" .. ;)

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