Late 2012 iMac - Sluggish "Jerky" Performance

Discussion in 'iMac' started by uptownnyc, Mar 21, 2016.

  1. uptownnyc macrumors 6502

    Mar 28, 2011
    I have a late 2012 iMac with a 3.4Ghz i7, 32gb of RAM, and the 3tb fusion drive. Recently it's felt increasingly sluggish while performing basic tasks (browsing the web, switching between apps, etc.). If I had to describe how it feels, it feels "normal" for a little while, then it seems to seize up and pause for a couple seconds, then it'll unlock again and feel like it's normal again.

    I've tested the drive using the Apple utilities FirstAid tool, and it's fine. But the drive is approaching being totally full. It currently has about 65gb free space. Is it possible that the sluggishness is being caused by the lack of drive space?

    Any other way to help determine what's causing this problem?

  2. Samuelsan2001 macrumors 604

    Oct 24, 2013
    Yes it's very long kelly that the slowdown is due to lack of space on the 3tb hard drive. Maybe an external drive to archive some files too would be a good place to start.
  3. JSC macrumors member

    Nov 25, 2007
    Phoenix, AZ
    When I've had a similar experience with my iMac, if Apple's Disk Utility didn't solve the problem or said there were no problems, I then use Disk Warrior 5.0. It is more powerful and has always fixed the problem which could be a directory issue. Also, have you cleaned out your browser cache? It could be sucking up your memory too.
  4. Fishrrman macrumors P6


    Feb 20, 2009
    What I'd suggest doing:

    1. Get an external drive large enough to hold everything
    2. Create a CLONED BOOTABLE BACKUP using CarbonCopyCloner
    3. Boot from the backup
    4. (this is the important step) "DE-FUSE" the fusion drive. That is, "split it up" into a separate SSD drive and a separate HDD drive. Instructions can be found on the net.
    5. Install a clean copy of the OS onto the SSD
    6. Create a NEW user account for yourself
    7. Migrate your applications ONLY to the SSD using Migration Assistant
    8. Now, carefully begin "moving by hand" stuff from the external drive.

    SOME things you want to put onto the HDD -- such as your overgrown libraries of music, pictures, movies, etc.

    OTHER things you want to move into your home folder, such as "library items", etc.

    The idea will be to keep the SSD "lean and clean", so that the seldom accessed stuff stays on the HDD.

    Do this properly, and you will get "SSD speeds" booting and running normal things, because CORE storage (the "engine" that drives fusion) won't be busy and overloaded trying to manage back-and-forth between the SSD and the HDD.

    You will assume such responsibilities yourself.
    But I absolutely guarantee that you will once again have a speedy Mac.

    My opinion only.
    Others will disagree.
    Some will disagree vehemently.
  5. bent christian, Mar 21, 2016
    Last edited: Mar 21, 2016

    bent christian Suspended

    bent christian

    Nov 5, 2015
    Unless the user has a specific need to, I advise against defusing a Fuson drive. Overall, I think the OP would probably not realize much benefit. The problem appears to be a hard drive is too full. Simply splitting up the same data across the same drives will not change any of that.

    uptownnyc: You need more free space. Using OSX, IMO, you want 20%-15% free space optimally. That is 450GB-600GB in your case. Can you archive to disc or move some things off to an external drive? Another option is to keep everything where it is, clone your applications and Home folder to an external SSD and boot externally. This would give you around 400MB/s write and 430MB/s read speeds, which is probably only slightly less than the peak of the SSD speeds you see now. Having a full SSD boot will mean those speeds are not constant. There is an advantage. Booting externally means you will also have a internal dive faster than any spinner. Splitting up the Fusion drive is the absolute last thing I think you should do, after all other solutions have failed.
  6. Fishrrman macrumors P6


    Feb 20, 2009
    bent christian wrote:
    "Unless the user has a specific need to, I advise against defusing a Fuson drive. Overall, I think the OP would probably not realize much benefit."

    I strongly disagree.

    Fusion works by "offloading" seldom-accessed files from the SSD to the HDD, and then "reloading" more-frequently-accessed files.

    With as much space used as the OP reports, I'm going to guess that the SSD portion of his fusion drive is also "at capacity". Perhaps this is pushing his VM disk writes "out to" the HDD. And with the HDD full, and probably EXTREMELY fragmented, the drive's heads are jumping back and forth all over the place for VM calls.

    By "splitting" the fusion drive, the owner can control just what goes onto and on with the SSD. Of course the slow HDD is still there, and it's still slow, but now the OS can run, VM and all, "unfettered" (so to speak) by the speed of the HDD.

    All that counts is the speed of the SSD, and even a 128gb SSD will run very fast on the internal SATA bus.

    The OP must however take care to NOT "fill up" the home folders on the SSD drive with lots of "stuff" that will use up its space. This will guarantee a good amount of free space for VM swaps, temp files, etc.


    For the sake of argument, let's say the OP THREW OUT just about ALL of his files, then split the fusion drive, and installed the OS, apps, and small home folders on the SSD drive only -- leaving the HDD "empty" and untouched.

    Would you still argue that the SSD drive would not run at its native SSD speeds?
  7. bent christian Suspended

    bent christian

    Nov 5, 2015
    The solution of splitting the two drive completely sidesteps the most likely root of the problem: only having 2% free drive space.

    A user will almost never be as efficient as the Fusion software solution. We are unable to move files block-by-block and we only have estimated guesses of our file usage. There are good, very specific reasons why a person might split the drives. We can't apply those here, it's bad advice.

    Free up some space, get your Fusion down to 15% and see if the speeds changes. I think it will.

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