CAUTION! SSD Drives and Yosemite [u]

Posted on by Sudd

UPDATE 6/30/2015. As reported by Ars Technica and confirmed by Apple, today’s OS X 10.10.4 update “has added a command line utility that can be used to enable TRIM on third-party SSDs without having to download and install anything. Called trimforce, the utility can be executed from the OS X terminal, and it requires a reboot to start working.”

“TRIM helps SSDs out by telling SSDs which pages can be marked as stale when an operating system deletes files (something the SSD ordinarily would have no way of knowing). It’s by no means a requirement, but it’s helpful and could potentially help the performance of an SSD as it ages.

“The scary warnings about trimforce are likely in place because not every disk implements TRIM in the same way, and older SSDs might behave oddly or in ways that OS X doesn’t expect when told to TRIM pages. If you have a relatively recent SSD, though, there shouldn’t be any problem enabling TRIM via trimforce—especially considering that same SSD in Windows or most current Linux distributions would already be using TRIM.”

Read the entire article here.


If you own a 3rd-party SSD (Solid State Drive) unit and are running a version of OS X 10.10.3 or earlier (Yosemite) – you NEED to read this.

If you own an Apple SSD or Fusion drive, this article does NOT apply to you.


Last week, on the Digital Production Buzz, OWC CEO Larry O’Connor discussed a critical problem where computers containing a 3rd-party SSD drive are unable to work properly under Yosemite. And, in some cases, the system won’t boot at all; resulting in a gray startup screen.

The issue revolves around Trim utility software used by the SSD drive.

NOTE: Listen to his complete interview here.


In order for an SSD system to work properly, the operating system needs to “clean” the unused contents of an SSD drive whenever you add or delete media. Further, the OS needs to know what parts of the SSD are available to store new data.

This process is handled by Trim software. The difficulty is that Apple only supports Trim on its own SSD drives. If you use a 3rd-party drive, you have to use 3rd-party software to get the performance you need from the SSD.


OWC writes in its blog:

“…Support for Trim is based on the operating system and the SSD manufacturer. Microsoft Windows began to natively support the Trim command for SSDs in Windows 7. Apple added Trim support in 10.6.8, however Apple does not natively support Trim on non-Apple SSDs.

“Trim is an operating system-based command for SSDs that is activated when you delete a file on the SSD. When you delete a file from your computer, Trim notifies the SSD that the location of the deleted file no longer contains valid data. Trim then works in conjunction with the SSD’s garbage collection process to move both valid and invalid data from the old block to the new block. Having Trim enabled prevents the invalid data being moved. This in turn frees up space on the SSD and reduces write amplification. Now the “moving company” only needs to focus on moving the current tenants and ignore the vacant homes.”

NOTE: Read OWC’s entire blog here:

One of the most popular Trim tools is “Trim Enabler” from Cindori Software. Cindori continues the discussion:

“Every time you delete a file on your computer, the data still stays on the drive in segments called blocks. These blocks are not deleted until you need to use them again to write new data. Due to technical limitations in the NAND Flash design, only whole blocks can be deleted. This means that when you need to write new data, the SSD must perform time-consuming cleaning and maintenance of these blocks before your data is written. With Trim, your blocks can be cleaned instantly when you delete the data, leading to much less operations during the writing process which gives you better speeds and minimizes the wear on the drive.”

Cindori continues:

“In OS X 10.10 (Yosemite), Apple has introduced a new security requirement called kext signing. (A kext is a kernel extension, or a driver, in Mac OS X.)

“Kext signing basically works by checking if all the drivers in the system are unaltered by a third party, or approved by Apple. If they have been modified, Yosemite will no longer load the driver. This is a means of enforcing security, but also a way for Apple to control what hardware that third party developers can release OS X support for.

“Since Trim Enabler works by unlocking the Trim driver for 3rd party SSD’s, this security setting prevents Trim Enabler to enable Trim on Yosemite. To continue to use Trim Enabler and continue to get Trim for your third party SSD, you first need to disable the kext signing security setting.

“It is important to note that the kext-signing setting is global, if you disable it you should be careful to only install system drivers from sources that you trust.”

NOTE: Read their entire FAQ here:


The only workaround is to turn off kext-signing, which, as Cindori describes is similar to “taking a sledgehammer to crack a nut,” because this affects every driver on your system, not just the SSD.


If you have a 3rd-party SSD drive, check with the manufacturer to see if it works on Yosemite. (Assume that it does not.) At this point, you have two options:

  1. Replace the drive with a supported Apple SSD rive, or a non-SSD system.
  2. Turn off Kext signing. (See the Cindori link at the bottom of this article for instructions.)

Also, let Apple know – via Send Feedback to Apple inside Final Cut Pro, or other Apple applications – that they need to reconsider their policy. Speed is essential to all media creators. Apple needs to find a way to support Trim functions on all SSD drives, not just Apple systems.


This is a big deal. If you have a 3rd-party SSD, you have the potential to be dead in the water on upgrade. For this reason, please contact the manufacturer of your SSD system – and read the supporting articles – before upgrading to Yosemite. Make sure you KNOW that your drive will work before you have problems.

Remember, Apple-supplied SSDs work fine. The issue is only with 3rd-party SSD drives.


OWC reports that their SSD drives don’t need Trim. You can read their entire article here:

Read the entire Cindori Software FAQ here:

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92 Responses to CAUTION! SSD Drives and Yosemite [u]

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  1. Colin says:

    Hi Larry,

    You can enable TRIM on non-Apple SSD’s, and here is how:

    • LarryJ says:


      Thanks for sharing this link.

      I need to STRESS that working in Terminal is not to be taken lightly. You are patching the operating system.

      If Terminal is foreign territory, I would suggest you not do this. If you are comfortable in Terminal, this provides an intriguing work-around.


  2. Andrey says:

    Where do I get a proper list of apple-certified drives that will support TRIM in Yosemite? Contacting Samsung for example might take months.

    • Colin says:


      Only SSD drives that are Apple identified will have TRIM enabled. The script referenced above does some trickery to the IOAHCIBlockStorage kernel extension that bypasses the test to see if the drive is an Apple identified drive (I think it’s the serial number or Model) and loads the kernel extension regardless.

      If it’s not an Apple drive (OEM) it won’t support TRIM without TRIM enabler, or hacking the kernel.


  3. Chris says:

    I just talked with Crucial and they said regarding their SSD drives… “It does not need TRIM. It has awesome garbage collection that is so spectacular in every way that it’s entirely self-sufficient.” So It has some built in firm ware functions that take care of it when the drive is idle. So no TRIM needed on Crucial SSD drives.

  4. Pingback: Angelbird SSDs for Mac with TRIM support for "Yosemite"

  5. Pingback: Apple,Yosemite and Trim

  6. Rod Mitchell says:

    I just shoot using SSD’s – All I need to do is transfer the video files from SSD to hard drive via a Mac… Does this trim issue afffect me?

  7. rsrzr says:

    You don’t need TRIM enabled on your MAC and don’t disable KEXT. What you can do is create a batch job that runs while you sleep that executes the TRIM function. You need TRIM for any flash type of product, but you have options on how to implement it. Normally you implement TRIM on the mount command. By not enabling TRIM at the mount stage, you could actually improve performance during usage while a little degraded performance will occur when running the batch job.

  8. geoff says:

    what do you do if you already installed? or tried to? i have a samsung ssd as startup drive and yosemite hangs on upgrade restart at gray/white screen. i can do nothing now. shuts down when i push power button. no “special” start commands work. machine is on but not accessible.

  9. Mark M says:

    I think that publishing this article is a great disservice; this article misstates the actual issue.

    The issue is that Yosemite introduced a new security requirement called kext signing. This basically means that only Apple supported drivers are supported IF kext signing is ENABLED. So if you have a 3rd party TRIM, then driver will not be loaded. So to avoid this, you should disable kext sighing. See for a complete discussion.

    Another thing to note is the you really don’t need the TRIM to use a SDD. You only need TRIM to extend the life of the SDD. As far as the OS is concerned, it’s a non issue, because the SDD looks like another hard drive to it, which is by the design of the SDD. The SDD controller take care of logic involved for reading/writing to the SDD, which unlike a regular hard drive where the OS takes care of most of that logic.

    I’m running Yosemite on a mid 2010 MacBook Pro with a Samsung SSD 840 EVO SDD as the boot drive, and never had an issue (either with TRIM or with out TRIM).

    • geoff says:

      just agreeing with Mark M here. all true. i learned the same upon further investigation. for me I just had to reset pram and then install completed. of note, i still have trim enabled but clearly i would say not necessary. but system works fine.

  10. lb says:

    My Intel SSD 520 480GB got bricked by this problem somehow. It won’t power up, and neither a Mac or a PC now recognizes it. Recovery failed for me with error 2000D so I thought about mounting the drive on another system and manually removing trim enabler. But mounting failed, it would accept my whole disk encryption password but not mount the filesystem. I manually removed the encryption (it took many hours while mounted over usb 2.0) and in the morning the disk was bricked.

    Thanks Apple for not fixing your installer to catch unsigned 3rd party kernel extensions during install and disabling them.

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