SSD addition to MacBook Pro running ML

Discussion in 'OS X Mountain Lion (10.8)' started by jc244, Oct 4, 2012.

  1. jc244 macrumors newbie

    Sep 29, 2012
    Hi I was hoping to seek some answers for a question about TRIM Support for SSDs added to my macbook pro. Currently I have an SSD installed with Apple firmware, it was purchased as an upgrade when I purchased the macbook pro. The SSD has TRIM enabled automatically. I want to add another SSD in the optical bay and would like to run the two in RAID0 configuration. If the SSD is third party, will the configuration have trim enabled because the one of the SSDs has TRIM enabled automatically? What if both drives have TRIM, will the RAID0 configuration have TRIM enabled in that case?

    Thanks for your help.
  2. Weaselboy Moderator


    Staff Member

    Jan 23, 2005
    I can't answer your RAID question, but no aftermarket SSD is going to have TRIM enabled without running the TRIM hack.
  3. Menneisyys2 macrumors 603

    Jun 7, 2011
    1, as has been stated, you need to explicitly enable TRIM.

    2, are you sure RAID will work? I've been hearing quite bad things about system SSD's in the bay (booting problems and the like). Hope it won't crash your entire system.
  4. Wolfpup macrumors 68030

    Sep 7, 2006
    Okay, so 10.8 still does *not* support TRIM except on Apple OEM drives? (Lame!)

    For me that would pretty much rule out using any SSD except Intel's 320 series, as it does pretty well without TRIM-like write performance halves, but would still be fast, and (under fairly normal use) shouldn't be killed or anything. Samsung's drive is awful without TRIM. Even Crucial's drives and Intel's 520 aren't good without TRIM either.
  5. benthewraith macrumors 68040


    May 27, 2006
    Miami, FL
    The Trim Enabler works fine with the 320 series.
  6. Wolfpup macrumors 68030

    Sep 7, 2006
    Guess that's this:

    Good to know, though I'm always paranoid about installing stuff like that.

    I *think*/hope the 320 series ought to handle being used without TRIM okay, though unfortunately the 320 is a lot more expensive than the 520 or Crucial's drives.
  7. jc244 thread starter macrumors newbie

    Sep 29, 2012
    So to follow-up. My two samsung SSDs are in a software RAID assisted by disk utility and after running the terminal commands to enable TRIM, it does show that each disk has TRIM support. This is when I check it in my system report and look at the serial ATA device tree. I don't know the details of how it actually works in this configuration but I guess seeing that it says it's enabled is good enough for me.
  8. TheTrueGeek macrumors newbie

    Nov 24, 2012
    TRIM will only work with one brand at a time

    The way OSX determines whether to enable TRIM or not is by reading the vendor string from the drive and comparing it with an expected value hard coded into the driver. The hack changes the expected string from APPLE to whatever your drive returns. If you have two different drive brands installed, only one can compare equal to the driver's hard coded string, so only one will be recognized as an SSD and be provided with TRIM.

    To get around this, you would have to write a shim that loads before the non-comparing drive is queried, that intercepts the return from the drive and passes the expected string to the Apple disk software. Or, of course, Apple could remove the stupid proprietary test, but I wouldn't hold my breath waiting for that to happen.

    The use of TRIM may speed up writes as the drive fills, but its main purpose is to extend the life of the drive by reducing wear caused by rewrites. Its main benefit will be seen years down the road when the drive does not fail as early as it otherwise would. Also, it is only useful if the drive is used in a way that files are deleted or modified frequently. Extending a file does not count as modified in this case, nor does creating new files. Rewriting a file counts as modified even if it wasn't changed.

    There are explanations of the details of what TRIM does and why it is useful to be found elsewhere on the web. Google is your friend.

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