Late 2015 Retina iMac unusable after periods of inactivity

[Grymbok]

"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)

Done that, just getting the same error on the new name.

 

[Grymbok]

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.

That's a very good point! Thanks.

 

[DDetloff]

Grymbok,


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.

I also have a late 2015 27" iMac and have been wondering about after Apple stops security updates in a couple years for this iMac. Will Anit-Virus software from another company take the place of Apple's security updates? I'm retired and don't look forward to having to update my iMac because of the cost for a new one.

 

[pshufd]

I also have a late 2015 27" iMac and have been wondering about after Apple stops security updates in a couple years for this iMac. Will Anit-Virus software from another company take the place of Apple's security updates? I'm retired and don't look forward to having to update my iMac because of the cost for a new one.

Learn best practices for security. I have old Macs running High Sierra and El Capitan and they are completely usable - just be careful what you do online. My personal favorite to scan is Malwarebytes.

 

[DDetloff]

Learn best practices for security. I have old Macs running High Sierra and El Capitan and they are completely usable - just be careful what you do online. My personal favorite to scan is Malwarebytes.

Thanks. I'm already careful about online activity and use the free version of Malwarebytes. Sounds like I'm on the right path. Like you, I don't have any reason to update my iMac since the software I use meets my needs just fine. Maybe someday that will change, just hope that's far down the road.

 

[pshufd]

Thanks. I'm already careful about online activity and use the free version of Malwarebytes. Sounds like I'm on the right path. Like you, I don't have any reason to update my iMac since the software I use meets my needs just fine. Maybe someday that will change, just hope that's far down the road.

The usual main interface with the internet is the web browser and those fortunately have a fair amount of antimalware protection or you can add extensions to do that. I am a fan of old equipment as I hate to see it go to waste. I do plan to sell my 2009 and 2010 iMacs one of these days but it's nice to be able to use them in Target Display Mode or just as a loaner computer if someone needs to borrow one for a while.

 

[zarmanto]

Thanks. I'm already careful about online activity and use the free version of Malwarebytes. Sounds like I'm on the right path. Like you, I don't have any reason to update my iMac since the software I use meets my needs just fine. Maybe someday that will change, just hope that's far down the road.

If you're using best practices and if your computer hasn't shown signs of imminent hardware failure, you'll probably be okay for awhile yet.

I still have a 2012 iMac in my basement, which is currently living it's "second life" so to speak. It was my primary machine until about 2019, and now it has a 2TB SSD where there used to be a failing 3TB HDD. Not only is it humming along fairly nicely, it also sometimes serves as a work-from-home computer for my father-in-law... and he has on multiple occasions commented to me that it outperforms his two or three year old Windows laptop.

Just keep using it until the wheels fall off, right?

 

[Grymbok]

Finally got Time Machine working! It's doing a first back up (I nuked the old backup history thinking that might be part of the problem, but it didn't help) so that's taking several hours, but hopefully after this I'll be 100% up and running with the External SSD.

In case anyone has the same problem in the future and finds this thread - I had to use Disk Utility to rename the hidden "Macintosh HD - Data" volume as well as changing the drive's top level name. I've no idea why that worked considering that Time Machine was telling me the problem was something else, but it did.

Once I have Time Machine up and running successfully I'm going to try to stop auto-mounting of the old HDD at boot up time.

 

[Anthony Z]

You could've kept the old HDD. Just run: diskutil APFS defragment \dev\disk#s# status to see if it is defragmented and diskutil APFS defragment \dev\disk#s# enable to enable defragmentation

 

[zarmanto]

You could've kept the old HDD. Just run: diskutil APFS defragment \dev\disk#s# status to see if it is defragmented and diskutil APFS defragment \dev\disk#s# enable to enable defragmentation

This presumes that the only issue causing his HDD's performance degradation was fragmentation. This is not at all a given, particularly since it was in a Fusion configuration, meaning that the most frequently accessed data wasn't even being read from the HDD, but rather, from the small SSD portion of the Fusion array.

Of course, even if we were to accept fragmentation as a plausible source of his problems: given the age of the computer, it's a very reasonable expectation that hardware failure is not far off for that HDD. So in addition to restoring normal performance, the external SSD was also a good way to do a bit of low risk future-proofing for that aging computer. I think he made a very reasonable choice.

 

[Grymbok]

The old HDD is still in the body of the iMac, I’m using an external SSD, there’s been no surgery here.

If I leave the old HDD mounted I still get slowdown problems after a few hours. If I unmount after booting that doesn’t happen. That’s why I’m planning to stop auto-mounting.

 

[zarmanto]

... If I leave the old HDD mounted I still get slowdown problems after a few hours. ...

Wow... yeah, that's sounding more and more like a failing disk... though, a reformat of the drive may be worth a try at some point, to see if maybe it's just a corrupted partition.

Mind you, hardware failure is still the most common cause of data corruption, so I wouldn't keep your hopes up too high... but even absent hardware failure, the partition mapping data on any drive can become corrupt over time by things like OS crashes and/or unexpected reboots. (I've seen it quite a few times, myself.) And seven-ish years... that's a whole lot of time, and a lot of potential opportunities for data corruption.

As to preventing automount of the internal drive... it's a bit of a Band-Aid, but I can see the appeal. You may have already found this thread over on Apple's discussion forum, but just in case... here's the suggestion I found over there, with minimal cleanup for (hopefully) easier reading:

1. Make sure the disk you want to prevent mounting at boot is mounted.
2. Launch Terminal.
3. Open Disk Utility, select the drive, click info, and copy its UUID
4. Type cd /etc in terminal and press enter
5. Type sudo vifs and press enter
6. Enter password
7. To add a new line, use the arrow keys to move to the end of the document and press the o key to append a new line and enter edit mode.
8. Type the following and press return:
   • UUID=(Your number from step 3 above) none hfs rw,noauto
9. Press escape and then Shift-ZZ.
10. Type sudo automount -vc and return
11. Quit Terminal

 

[Grymbok]

I figure I don’t plan to use the drive for anything so no need to have it mounted. But yeah makes sense to flatten out the partition table (it current has a Windows partition I never use too) and reformat to see if that makes it play better with the new install.

I’d like to get at least another six months out of this iMac, preferably a couple years if I can.

 

[Fishrrman]

If you no longer need to use the internal fusion drive, you could erase it.

Just leave it erased, empty, "un-used", but "in-place".

Another option:
Erase it, then make it a backup of the external SSD boot drive.

 

[Nicole1980]

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?

You should shut it down if you don't intend to use it for a day or two. It's not clear from your post if you EVER shut it down. Sometimes a full shutdown and restart is all it takes to clear out some mysterious issues.

 

[zarmanto]

You should shut it down if you don't intend to use it for a day or two. It's not clear from your post if you EVER shut it down. Sometimes a full shutdown and restart is all it takes to clear out some mysterious issues.

Fascinating factoid: This advice doesn't necessarily apply to Windows. Apparently, if you want to "clear out" everything on a modern Windows system, you actually have to perform a direct reboot action, rather than a turn-it-off-and-on-again action, since the default behavior in Windows is to hibernate upon shutdown... which means that it just reloads everything exactly as it was in your last session when you turn it back on.

But yeah... I think this is still good advice for macOS users. At least, for now...