Apple HDD not there?

[bear100]

Hey all

i am having an issue with my late 2015 iMac, for some reason it crashed a few months ago and would not boot up ( I think it was a result from an automatic update?), I ended up rebooting over the internet which took the machine back to factory Os, I then downloaded Monterey, but ever since the machine has been very slow, restart can take up to 10 mins, bluetooth takes ages, airplay has stopped working and my USB sockets have stopped (they power everything but no external is identified in disc utility), i can see the mac recognises what's plugged in but nothing will work.

So i want to try and reset it back to factory and start again, here's the trouble - when I restart in recovery to erase the Apple HDD it doesn't appear in disc utility? i have instead an Apple media drive and a container disk? so then try to reinstall Os Monterey when it asks to choose a disc nothing appears?
in standard disk utility Apple HDD shows. not sure how to proceed?

 

[Fishrrman]

Does your Mac have a fusion drive?
Or is it a platter-based hard drive only?

If it's a fusion drive, I'm thinking the crash may have "split it apart", and the re-install of the OS went onto the HDD portion of the fusion drive (instead of onto the SSD portion).

The HDD portion of the fusion drive is MUCH SLOWER than the SSD. Hence, the speed decline.

Do this for us:
a. open disk utility
b. go to the "view" menu and choose "show all devices" (this is VERY important)
c. take a screenshot of what it shows, and post it here.

 

[bear100]

Thanks for the reply, this is what is in disc utility, how would I know if I have a Fusion Drive?
Thanks

 

[Fishrrman]

That doesn't look like a fusion drive to me... just a platter-based hard drive.

If you'd really like to speed it up, the easiest solution would be:
- Get a USB3 SSD (I'd suggest a USB3.1 gen2 SSD like the Samsung t7)
- Install the OS of your choice onto it
- Install your apps and accounts on the SSD
- Boot and run the iMac from the SSD

Use the internal drive as a backup of the SSD (a cloned backup would be a very good way to do this, so you'd have a 2nd boot source for "insurance")

 

[bear100]

This is what the terminal shows me (just read a post on here how to find out if you have a Fusion Drive) does this suggest a fusion drive? and does it look about right?
Your suggestions sounds good thanks but how do I reset it? As mentioned my USB sockets won’t recognise anything plugged in

 

[Fishrrman]

I would boot to INTERNET recovery
Command-OPTION-R
at boot

Then, I would use disk utility to COMPLETELY ERASE the internal drive.
MAKE SURE that when you use disk utility, IF there's a "view" menu, you MUST go to it and select "show all devices" to see the physical internal drive in "the list on the left".

Once that was done, I'd open the OS installer and accept ANY OS that it offers to install.

A Mac that boots and runs (regardless of what OS is on it), is far better than one that won't.

 

[MacCheetah3]

Based on the specs, a 2TB configuration should be a Fusion Drive.

iMac (Retina 4K, 21.5-inch, Late 2015) - Technical Specification - Apple Support

support.apple.com

iMac (Retina 5K, 27-inch, Late 2015) - Technical Specifications - Apple Support

support.apple.com

However, it doesn’t appear that way on your system (e.g., I’m not seeing a second drive, SSD)

In Terminal (where you entered diskutil list), what does it show when you enter:

diskutil corestorage list

 

[bear100]

Hi, I’m sure when I bought the machine the sales person said it had a Fusion Drive and I got all Tony Stark and excited about it!

When the crash happened I was on an expedition in Barcelona and the wife googled and set the machine, to be honest don’t think it was done right.

Below are some pics just taken

 

[ryman145]

Hi, I’m sure when I bought the machine the sales person said it had a Fusion Drive and I got all Tony Stark and excited about it!

When the crash happened I was on an expedition in Barcelona and the wife googled and set the machine, to be honest don’t think it was done right.

Below are some pics just taken


View attachment 2147544 View attachment 2147543

I have this exact issue right now too with my 2017 iMac. I posted a similar post as I keep getting kernel panics because of this issue. I will be following and will let you know if I find a fix

 

[MacCheetah3]

Hi, I’m sure when I bought the machine the sales person said it had a Fusion Drive and I got all Tony Stark and excited about it!

When the crash happened I was on an expedition in Barcelona and the wife googled and set the machine, to be honest don’t think it was done right.

Below are some pics just taken


View attachment 2147544 View attachment 2147543

The No CoreStorage logical volume groups found means there’s no Fusion Drive configured.

Back to the confusing part: no apparent SSD.

An Apple Fusion Drive has two components, an SSD and an HDD. In your screenshots, we can see the HDD, ST2000DM001. However, there should be another physical drive, APPLE SSD SM0128G,

Something like this:

You can find this information on your iMac using these instructions:

Get system information for your Mac

In System Information on your Mac, see details about hardware, network connections, and software. You can also create a system report.

support.apple.com

Ensure you click on/select SATA/SATA Express in the left column.

 

[bear100]

ahh maybe the Fusion Drive wasn’t set up after the crash?

This is what is says on System Report - SATA

 

[rpmurray]

Looks like you may have had a Fusion drive but the SSD part failed. Now you're running off the HD and have it formatted as APFS which will be noticeably slower than the Fusion or if the HD was formatted as HFS+. Since you're running Monterey you can't reformat as HFS+ because the newer OS requires APFS for the boot drive.

If you're handy with tinkering with electronics you could open up the iMac and replace the SSD with an adapter and an NVMe SSD. If not, then the best solution would be to get an external NVMe and boot from that. Some people will steer you down the USB3 external route, but I've always found them to be a bit flakey (the unexpected dismount problem), so I go with a Thunderbolt external which in my case had been much more reliable.

 

[Fishrrman]

It's not worth the money to buy a thunderbolt drive for an iMac that's now approaching 8 years old.

A drive like the Samsung t7 SSD will do fine.
This is a USB3.1 gen2 drive that is backward-compatible with the USB3 on the 2015 iMac.

Use it to boot and run the 2015 iMac now.
When the time comes to move up to another Mac, you can "take the t7 with you", and it will run FASTER on the newer Mac with USBc.

 

[MikeG17901]

If your model is MK462LL/A, it's probably a 3.5" drive (desktop size). However, you can replace with a 2.5" SSD and an adapter (or just 2-sided tape it to the chassis). They are easy to replace - check Youtube or iFixit. Less than 1/2 hr required. Make sure to get an screen removal and adhesive kit off of Amazon. They are less than $10.