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. Stefan says:

    Was using a Crucial M4 SSD on a older MacBook Pro without any problems on Mavericks. I never updated to Yosemite but a security update was applied. I am running OS X version 10.9.5. Booting from a USB works fine but trying to boot from the SSD only gets me to gray screen. I ran disk utility, reformatted drive, and reinstalled from a current backup. Never would boot. Started reading about all the problems with Macs and SSDs and said the heck with it. Went and bought a regular hard drive and things work fine. Going to put the SSD in my windows laptop. Windows has no issues with it. Just another case of Apple making their crap hard to use with anything other than Apple stuff. This is my second MacBook Pro cause the original one had processor that wouldn’t support the current OS. And I have an original Ipad that won’t upgrade the iOs as well. Thanks Apple.

  2. While not SSD drives, I have 3 external hard drives that I use for graphics storage and my Time Machine. Since upgrading to Yosemite (HUGE mistake), one of my drives has been acting up. It mysteriously disappears from Finder yet can be seen in Disk Utility. It comes back for a while then disappears again for a while. Apple Care was no help and seemed mystified. I have the files backed up, it is just the idea. I complained to Apple, they sent me to WD who then said it was an Apple problem! Now I am afraid to buy another external for fear it will happen again. At least I learned my lesson and I will not upgrade OS X right away!

    • Larry Jordan says:


      There was a problem reported a while ago now that Western Digital drives used software that had problems with Yosemite. I can’t say whether that is an issue with your hard drives. However, if you are using Western Digital, you might inquire from them, whether this issue affects your hard drives.

      It may be that they need an update of some sort.


      • Thanks Larry. That is precisely the case however WD currently has no plans to provide a Yosemite compliant driver (nor any wag of when they might do that) which leaves myself and many like me in a bit of a lurch.

        • Larry Jordan says:

          Sigh… Sorry to read that.

          Well, at least we know what the problem is. And this is a good caution for people running Yosemite to avoid Western Digital drives for a while.


    • Jay_S says:

      I pretty much exclusively run WD in my Mac Pro (internal and external)… Is there any clarification as to which WD drives are impacted (or is this just another reason to stay on Mavericks). Is this ALL WD drives or only certain ones.. Would be good to know which we’re talking about..

      • The one I am having issues with is a My Book Studio 2TB. My other WD 1TB and my 4TB Seagate are both working properly. The 2TB drive comes and goes. It will work for 2-3 days, sometimes, and then I get the message that the drive could not be read. I unplug it and leave it sit for a while (turning it off doesn’t do the trick), then I plug it back in and it will work for a time. I’ve transferred everything off of it. I had lengthy discussions with AppleCare and they are stymied as to what it could be.

  3. steve jameson says:

    Hi there! Following the thread regarding SSDs and Trim. I presume this applies to the2.5 inch drives as used in the Atomos Ninja and Shogun products ??? Can anyone comment before I make my purchase decision?
    Thanks to all!

    • evank says:

      Hi Steve,
      Just checking to see if you got any answers about this article applying to the SSD’s used in the Ninja. I am working with a ninja-2 and I had one of my ssd’s act up (the computer said that it could not read the drive and when I put it into the Ninja it said that it had a 0GB capacity ) and now I am just trying to figure out what went wrong.
      Do you erase/format your drives on your computer and then also reformat in the Ninja? I did that and I think it might be the reason I had problems. Now I just format in the Ninja only. Any ideas about why?

  4. Jay_S says:

    There is a ton of info here… A few points.. It seems (at least for now) that a solution for those with internal non-Apple SSDs that are on Yosemite, that a good housekeeping practice would be to turn trim on with Trim Enabler (just don’t reboot) and let the machine idle overnight. Trim and the drive’s internal housekeeping (whichever that it) should do some cleanup.. It’s a workable, if not perfect, solution.. Until there is something more substantive from Apple or drive manufacturer’s seems to be the only way to go..

    Something that may have been pointed out is that USB connected SSDs (USB 2 or 3) do not get any benefit from Trim as it won’t work across a USB connection. TRIM does work across Thunderbolt but I’ve not seen any reasonably priced 2.5 inch enclosures that are TB.. Especially compared to the price point of the UASP enabled Inateck (FEU3NS-1E make sure it’s the “E” version) ..

    I just upgraded my 2013 Macbook Pro with the OWC Aura 480 Pro SSD – but agree that I think even with Sandforce that TRIM is a desirable thing to run..

    Can I get some clarity on one post? Someone mentioned booting to Recovery and running disk utility repair disk.. Does this work regardless of TRIM or no TRIM being enabled? Also, does this help SSD Garbage Collection on External Drives? I have an Samsung EVO 840 (latest Firmware and Performance Restoration Run – Check Samsung site for details if you have an 840 class SSD).

    Thanks for the post.. Lots of good info..

    Jay S.

  5. Jay_S says:

    Relative to the comment about Western Digital drives.. I’m wondering if this is more the issue at hand?

    Seems Yosemite is having issues with externally connected drives.. Just spoke with Apple Tech support who said some of it is caused by a new preference in Yosemite where you have to “turn on” a view of external drives??

    Jay S.

  6. Wim Vandermaesen says:

    My recent experience with Yosemite was as follows : I just bought a 2nd hand 250 gb Lacie Rugged SSD (1,5 years old) The guy i bought it from did the Blackmagic speed test on a recent PB with thunderbolt. and it was perfect for me (250 MB/s write, 370 MB/s read). When i came home , i formatted the SSD hard drive and did a clean Yosemite install + update to 10.10.2. I also performed a time machine restore of my apps from my 1TB hard drive to the SSD.
    I did the black magic speed test and got very low and unstable write speed (varying from lowest 15 MB/s, but most of the time average of 50 MB/s) while the read speeds were still ok. I had read about the TRIM function and looked for an app to set it (it was not turned on). I used Chameleon SSD Optimizer for Mac to set the TRIM. After this, surprisingly, my speed was back to normal, and now i have again an average of 250 MB/s write, 370 MB/s read speeds.
    My guess is that the install procedure ‘fragmented’ the memory with lots of small files, necessary for the install, which get erased after or during install. After the restore of my time machine backup, those holes where probably filled with my apps and data… (Not sure how time machine reconstructs his files, but maybe it uses also some temporary storage on the target drive…

    Maybe somebody can clarify why i had this huge speed drop ?

  7. AppleLou says:

    Since this article showed up at Jordan’s newsletter I have not upgraded to Yosemite due to the confusion that I have. I have a new MacPro 2013 with original Apple SSD as the boot drive and an external Samsung EVO SSD connected thru Thunderbolt as a media drive for editing in FCPX. I don’t know at this point if I am affected by this incompatiblity
    or does this apply only to those that have 3rd party INTERNAL NON APPLE drives. What about my external Samsung is this affected too. I’ve never dealt with Trim before one way or the other. The Apple Forum has not been much help, can you clear things for me. I am still holding up to Maverick everything is good.

    • Larry Jordan says:


      I can appreciate your confusion. Based on what I’ve read, this situation affects non-Apple SSD drives whether connected internally or externally. However, not all drives are affected equally.

      I would urge caution, but the best advice I have is to contact your drive manufacturer and get their recommendation.


  8. Thad says:

    Wondering if anyone has tried this:

    Run your 3rd party SSD on Yosemite with kext enabled and no TRIM and once a week–or as needed– boot from a bootable Mavericks external and run a TRIM Enabler over night. In the morning, shutdown, remove the bootable external drive and restart with Yosemite.

  9. Alex Gant says:

    I have a Crucial M4 512GB SSD installed in my 27″ 2009 iMac running OS X 10.10. Every five or six months the systems dies. Literally, I’ll be part way through doing something and it just stops. No response from anything so all you can do is power down, restart in Recovery Mode and restore from a backup. I’m convinced that this is because of the lack of Trim support in Yosemite for third party SSD drives.
    In a way I can see why Apple has chosen not to support third party SSD drives and maintain tight control of Kernel extension signing but in other ways, it drives me up the pole and is another gripe that is pushing me towards Linux.
    For what it’s worth and I apologise if others have mentioned this (there are a lot of responses to this post now) but there is an Austrian company called Angel Bird ( ) who do offer third party SSD drives with Trim support even in OS X 10.10. Goodness only knows how they have managed it but they are a small ray of light within Apple’s ever darkening shroud of intrigue.

  10. Will Waters says:

    This is NOT AT ALL a problem with 3rd party ssd drives, this is an APPLE PROBLEM !

    Apple just switches off TRIM functionality for 3rd party drives because they want to make more profit by selling their drives.
    and this is not an unproven accusation, it is verified by checking the code in their driver: for all drives not reporting themselves as APPLESSD (by their firmwares) TRIM does simply get switched off. Even if those drive are top notch and support TRIM perfectly on any Windows machine. That’s Apple.

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