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Grymbok

macrumors newbie
Original poster
Dec 17, 2012
26
1
For the past week, my iMac (Retina 5K, 27-inch, Late 2015) has been unusably slow if it's left unused for too long. I selected "Prevent your Mac from automatically sleeping when the display is off", which seems to have helped a bit, but when I left the machine for a couple hours earlier today I had the same problems again.

What I get is either:
1) If waking from sleep sometimes it would crash and reboot after I enter my password, with the error message being Window Server not responding for 120 second
2) More generally, and since disabling sleep, what I get is unusably slow performance. Every click creates a beach ball, but eventually most will actually produce a respond after 60 seconds plus. The iMac generally stays responsive enough for me to be able to trigger a software reboot, but the most recent time it didn't.

I have a Fusion drive, and as this is my third iMac with a Fusion drive my suspicion is it might be to blame as that's usually what goes.

Disk Utility has found no errors. I booted in to Apple Diagnostics mode and that also found no errors.

I'll probably try a wipe and reinstall next but am worried that if the root problem is hardware I might end up in a worse state.

Anyone seen similar problems and can offer advice?
 
I have a suspicion that APFS slowdowns Macs with Fusion Drive or HDD.
Thinking that reinstall would help for some time because it will remove the filesystem.

You can test it by installing older macOS that utilizes Mac OS Extended rather APFS as a default file system (like High Sierra)
 
Personally, I have never been a fan of the whole "Fusion Drive" concept. The obvious benefit is that you improve the overall performance of the system with a small SSD alongside your spinning rust disk... but the disadvantage is that now you have two components which can potentially fail over time, where before you had only one. And of course, the failure of a drive is never immediately diagnosable; in my experience it has to already be really close to the point of total failure before the software diagnostics will start complaining about bad sectors and what-have-you. By that point, you've almost certainly already lost data, even if you don't know it yet.

I'd say get that Fusion Drive out of there, and replace it with a good sized SSD. They're much cheaper these days, so there's really no good argument for bothering with Fusion. Regardless of whether the cause is APFS or one of the two drive mechanisms failing, I think you'll definitely be better off with the single SSD in the long run.
 
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Grymbok,

Download Drive DX, which is free to try, and see if your drives are in good condition.
Here's the link: https://binaryfruit.com/drivedx
You can set it up so you'll have an icon for DriveDX in your menu bar. It'll have a green dot if all is well.
Excellent application for checking the health of your drives. Open the app and check out the stats on your two drives.


By the way, I also have a late 2015 iMac, 250GB SSD, that is my production machine. It's running quite well and I plan on continuing to use it for another couple of years.

Monterey is the last Mac OS that will work with your computer. I mention this because security updates will only be available for another 2 years once Mac OS 13, Ventura, drops this fall. Once the security updates stop for the late 2015 iMac I'll be retiring it, and replacing it, hopefully, with a new iMac Pro M3.
 
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Grymbok,

Download Drive DX, which is free to try, and see if your drives are in good condition.
Here's the link: https://binaryfruit.com/drivedx
You can set it up so you'll have an icon for DriveDX in your menu bar. It'll have a green dot if all is well.
Excellent application for checking the health of your drives. Open the app and check out the stats on your two drives.


By the way, I also have a late 2015 iMac, 250GB SSD, that is my production machine. It's running quite well and I plan on continuing to use it for another couple of years.

Monterey is the last Mac OS that will work with your computer. I mention this because security updates will only be available for another 2 years once Mac OS 13, Ventura, drops this fall. Once the security updates stop for the late 2015 iMac I'll be retiring it, and replacing it, hopefully, with a new iMac Pro M3.
Thanks, I’ll try that.

I’d missed that announcement about Ventura. Good to know. I’ve been thinking about upgrading but I’d rather not have the expense this year if I can avoid it, especially given the lack of a clear upgrade path for those of us used to a 27” screen.
 
Personally, I have never been a fan of the whole "Fusion Drive" concept. The obvious benefit is that you improve the overall performance of the system with a small SSD alongside your spinning rust disk... but the disadvantage is that now you have two components which can potentially fail over time, where before you had only one. And of course, the failure of a drive is never immediately diagnosable; in my experience it has to already be really close to the point of total failure before the software diagnostics will start complaining about bad sectors and what-have-you. By that point, you've almost certainly already lost data, even if you don't know it yet.

I'd say get that Fusion Drive out of there, and replace it with a good sized SSD. They're much cheaper these days, so there's really no good argument for bothering with Fusion. Regardless of whether the cause is APFS or one of the two drive mechanisms failing, I think you'll definitely be better off with the single SSD in the long run.
As @stradify noted, this iMac is coming to the end of its supported life, so I’m not likely to start trying to modify the hardware at this point! Thanks for your thoughts though.
 
Reminds me of how my late 2013 iMac behaved before I switched over to booting from an external SSD.

The advice I got was that the hard drive was probably starting to fail
 
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Reminds me of how my late 2013 iMac behaved before I switched over to booting from an external SSD.

The advice I got was that the hard drive was probably starting to fail
Ooh, I hadn’t realised external SSD booting was an option! That looks a pretty affordable upgrade, thanks I think I’ll look in to that further.
 
As @stradify noted, this iMac is coming to the end of its supported life, so I’m not likely to start trying to modify the hardware at this point! Thanks for your thoughts though.

Just wipe out the internal Fusion drive and boot your iMac from an external USB 3.0 SSD drive. It's simple as that.
Wiping out the internal drive also helps purging your machine of malwares, etc, which are designed to consume your processing power (causing the lag).
 
In hindsight I was so glad I got a 1TB SSD when I bought my 2014 iMac. I remember thinking the Fusion drive was a completely idiotic storage system, even though a 1TB SSD in 2014 was quite expensive.
 
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For the past week, my iMac (Retina 5K, 27-inch, Late 2015) has been unusably slow if it's left unused for too long. I selected "Prevent your Mac from automatically sleeping when the display is off", which seems to have helped a bit, but when I left the machine for a couple hours earlier today I had the same problems again.

What I get is either:
1) If waking from sleep sometimes it would crash and reboot after I enter my password, with the error message being Window Server not responding for 120 second
2) More generally, and since disabling sleep, what I get is unusably slow performance. Every click creates a beach ball, but eventually most will actually produce a respond after 60 seconds plus. The iMac generally stays responsive enough for me to be able to trigger a software reboot, but the most recent time it didn't.

I have a Fusion drive, and as this is my third iMac with a Fusion drive my suspicion is it might be to blame as that's usually what goes.

Disk Utility has found no errors. I booted in to Apple Diagnostics mode and that also found no errors.

I'll probably try a wipe and reinstall next but am worried that if the root problem is hardware I might end up in a worse state.

Anyone seen similar problems and can offer advice?
Fusion Drives generally blow. But mainly because spinning HDDs generally blow (though the Core Storage trickery also kind of blows, so I guess the whole damn package kind of blows.

Since that iMac is out of AppleCare, what I might do is take it to an Apple Authorized Service Provider and pay them money to replace the spinning HDD with a 2.5" SATA SSD and maybe even the stock SSD with either an OWC SSD or a Samsung SSD with an adapter. Either way, the one upshot to an older Fusion Drive equipped Mac is that you essentially have two drive bays in which to put in capacious SSDs. You can recreate the Fusion Drive between them (though, honestly, I'm not sure what practical benefit that'd have other than simplifying the number of volumes you have) or just have a primary boot drive with the faster SSD and a secondary projects/data/whateveryouwant drive on the SATA SSD.


Before doing any of that, I might run diagnostics to see what's happening. Make sure your RAM is properly seated and that there's nothing otherwise wrong with it. But, yeah, if it's the Fusion Drive and you want to keep that computer around (despite the fact that it can't run any newer than Monterey and that Monterey is only supported with security patches for the next two years), I might upgrade those drives!
 
"I have a Fusion drive, and as this is my third iMac with a Fusion drive my suspicion is it might be to blame as that's usually what goes."

Fool me once, shame on you.
Fool me twice, shame on me.

Why do you keep buying fusion drives, if you understand that their performance degrades over time?

Get an external USB3 SSD, and set that up to become your boot drive. Things will go faster...
 
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It’s lasted me seven years. Not sure I’ve ever had a computer for that long so I’m happy.

At the time Fusion Drives seemed like a good compromise between price and performance for me. I would not have wanted to pay 2015 prices for 3Tb of SSD!
 
Ooh, I hadn’t realised external SSD booting was an option! That looks a pretty affordable upgrade, thanks I think I’ll look in to that further.

Booting from the external SSD has made an amazing difference
 
It’s lasted me seven years. Not sure I’ve ever had a computer for that long so I’m happy.

At the time Fusion Drives seemed like a good compromise between price and performance for me. I would not have wanted to pay 2015 prices for 3Tb of SSD!
I also have a 2015 iMac with a Fusion drive. It works well, not as good as SSD, but the cost difference was significant. Having the 128GB SSD helps a lot compared to the later Fusion drives with a much smaller SSD.

Sometimes I boot to my Fusion drive, and sometimes to an external SSD. One option I am more cautious about updating to the latest version so I know I won't have issues, but then I am free to update the other as soon as possible. Both options perform reasonably well for me until upgrade to a newer Mac. I have the additional need of a Mojave installation for 32 bit apps, so have more than one external SSD I can boot into. Just leave your Fusion drive as is and do a separate external installation. You do not have to risk your existing setup.
 
Booting from the external SSD has made an amazing difference
I had a similar problem and My fusion drive died. Apple repaired it with a new fusion drive for $480 but it was still lagging and since they no longer offer support for this machine they refunded me $400 for the repair. They did recommend booting from an external drive which helped but was not ideal because I could only run it through the USB 3. In the end, I got a 2TB SSD kit from OWC for $300 and installed it and it's so much faster!

I'm sorry Macky-Mac, I meant to reply to the OP.
 
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Successfully moved to an SSD, have now unmounted the old Fusion Drive, and so far performance seems a lot better.

However Time Machine is sulking and won't run, saying I have two drives called "Macintosh HD", even after I've unmounted the old one. Any ideas?
 
Successfully moved to an SSD, have now unmounted the old Fusion Drive, and so far performance seems a lot better.

However Time Machine is sulking and won't run, saying I have two drives called "Macintosh HD", even after I've unmounted the old one. Any ideas?

Change the name of the new one to SSD or something.
 
Tried renaming and now it's telling me I have multiple drives called Macintosh SSD. I'm guessing something to do with the below is a problem but don't know how to fix?

Screenshot 2022-08-16 at 13.11.16.png
 
Tried changing on the desktop and now it's propagated the new name to all three levels in that snapshot and I still have the same error.

I'm wondering if I need to get a blank drive and start a new Time Machine history.
 
I'm wondering if I need to get a blank drive and start a new Time Machine history.
That would obviously be the safest solution.

Alternatively: Technically speaking, you currently have all of your data in three places, right? Your original internal Fusion drive, your Time Machine backup and your new SSD drive. I would assume you're not planning to go back to booting from the Fusion drive... so why not just reformat the Time Machine backup drive? You would of course lose the existing change history from your original drive, so you'll have to decide how much value that has.
 
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"Time Machine is sulking and won't run, saying I have two drives called "Macintosh HD", even after I've unmounted the old one. Any ideas?"

Change the name of the boot SSD.
Just click on the name, and change it, just like you'd change any file name.

Why not "Mac SSD" for a name?

(the Mac doesn't care what its drives are named -- that's for the user to decide)
 
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