Replacing standard HD with SSD in 27" iMac 2015

[JackP]

I'm about to purchase a used iMac 27-inch, Mid 2015 MF885LL/A.
Currently it has a standard mechanical hard drive in it.

I looked at the iFixit guide for replacing the SSD hard drive and it shows that if the unit is purchased with an SSD that Apple uses a M.2 Drive.

Questions:
1. If the unit came with a standard hard drive does it still have the M.2 socket (and is it full functional)?
2. Is there a significant benefit, that justifies the risk of disassembling the unit down to removing the main board, in using the M.2 socket over just replacing the mechanical SATA drive with a SSD?
3. Depending on the answer to #2, what SSD is recommended?

4. The last time I replaces a Mac mechanical drive with SSD was when SSDs first came out a few years ago. Under Lion I think I needed to install a kernal extension and do some other tweaks to get TRIM and other things to work. If I use High Sierra or Mojave and format the SSD as APFS (clean install of OS), is there anything I need to TWEAK to get optimal performance from the SSD?


Mac (Retina 5K, 27-inch, Mid 2015)
3.3 GHz Intel Core i5
16 GB 1600 MHz DDR3
AMD Radeon R9 M290 2048 MB
More specs

Thanks

 

[mikehalloran]

The iFixit site is good but... m.2 by itself doesn't mean anything and, no, I'm not going to explain all the differences. m.2 drives are not interchangeable although some can be with the right adapters.

There are 2 busses in 2013–2017 27" iMacs (not true of all 21.5"). One is a PCIe; the other is SATA III. An iMac can have a drive in either — the Fusion Macs have both.

The HD and Fusion iMacs have a mechanical hard drive in the SATA III buss. SATA SSDs range from 120G – 4T and are readily available. The buss speed has a theoretical max of 6G. SSDs get close while a single HDD cannot due to the platter speed. Besides the SSD, you want these when replacing the HDD: the OWC Temp sensor and the open adaptor.
https://www.amazon.com/OWC-Digital-Thermal-Sensor-Upgrade/dp/B00J42AFUA
https://www.amazon.com/Fenlink-Inte...coding=UTF8&psc=1&refRID=XPAHDHCDTH8R99BK8835

The PCIe buss can be either PCIe 2 (2013–4 iMac, portables, 2013—on Mac Pro) or PCIe 3x4 aka quad (2015–2017 iMac, portables). If you think of the quad as twice the speed of PCIe 2, you're good.

Interestingly, though the 2015 iMac has a PCIe 3x4 buss, Apple installed the slower PCIe 2 blade in the SSD and Fusion drives (only the MacBook Pro got 3x4 blades). These can take an NVMe PCIe 3x4 blade. You can install a Samsung 970 EVO into that slot with an adapter and turn it into a screaming fast machine. Essentially a 2017 with TB 2 ports. The 2T 970 lists for $579 ($499 on eBay) and smaller is available. The adapter runs $6 on eBay; $13 on Amazon.

The Apple blade uses a proprietary form made by Samsung. A system pull from a 2015 MacBook Pro drops in without an adaptor. When they show up on the market, a used 2T runs $1,500 while a 1T runs $1,000. As MBP owners are more likely to be upgrading, only the smaller blades are readily available.

As for a 2015 iMac, there are two differences between an MBP system pull and a 970+adapter. a) you have to loosen a speaker to get the adapter seated—it'll tighten up when done. b) the firmware on the 970 EVO requires OS 10.13 High Sierra or later.

 

[kretek]

Interestingly, though the 2015 iMac has a PCIe 3x4 buss, Apple installed the slower PCIe 2 blade in the SSD and Fusion drives (only the MacBook Pro got 3x4 blades). These can take an NVMe PCIe 3x4 blade. You can install a Samsung 970 EVO into that slot with an adapter and turn it into a screaming fast machine. Essentially a 2017 with TB 2 ports. The 2T 970 lists for $579 ($499 on eBay) and smaller is available. The adapter runs $6 on eBay; $13 on Amazon.

Do I understand you correctly that only the MBP would run at full speed PCIe 3x4 bus and not the iMac.

So if install the 970 Pro on my late 2015 iMac would not be of any real benefit than installing the 970 Evo.

 

[mikehalloran]

Do I understand you correctly that only the MBP would run at full speed PCIe 3x4 bus and not the iMac.

No. In fact, you misunderstood completely. Both have the same buss but Apple put the slower blade into the iMac. I could make many guesses as to why.

So if install the 970 Pro on my late 2015 iMac would not be of any real benefit than installing the 970 Evo.

That is the opposite of what I wrote.

This is the upgrade that turns a 2015 into a 2017 with TB 2 ports.

 

[kretek]

Ok great, thanks for clarifying.

 

[mikehalloran]

You're welcome. It's always a challenge to fit as much info into as little space as I can and still try to be clear. Where's the right spot between too much and not enough? Even though it made sense to me, I'm glad you asked so that I could clarify.

 

[JackP]

mikehalloran, thank you for your comprehensive reply.
Let me see if I got all of your points correct:

The SATA III interface 6GB/s and requires thermal sensor and mount

The PCIe 3x4 is about 5X quicker than the SATA III interface
M.2 Slot will definitely be on a 27" iMac 2015 (even if it came with a HDD)
The Samsung 970 EVO will work but requires an adapter, but I dont need any kernal extensions, drivers, etc.
Just format as APFS on High Sierra or Mojave

What adapter am I looking for if I get the Samsumg?

Im also considering a 500GB drive. Something like this should be as fast as the 1T model, correct?
it says 4 lane PCI (ie the OEM Apple Blade 500GB will fit and is PCIe 3x4)

Thanks so much again!

 

[mikehalloran]

If the seller is correct and it's a system pull from a 2015 model MBP, then yes. That is what is being advertised.

The only reason not to buy it is that the 970 EVO lists at $149 for a 500G exclusive of the adapter.
https://www.amazon.com/Samsung-970-EVO-500GB-MZ-V7E500BW/dp/B07BN4NJ2J

I notice that the above Amazon seller has the 2T for $100 over li$t. A number of resellers have run out in the last week—the 970 EVO 2T is a hot commodity.

This is the adapter for $11. All it does is convert the pin-out.
https://www.amazon.com/JSER-16pin-M...0937110&sr=1-1&keywords=970+evo+apple+adapter

 

[JackP]

Do you think the "tape" and opener tool iFixit sells is the best way to do the job or are they a waste of money? If so, what would you recommend in their place?

Thanks for all of your help.

 

[mikehalloran]

You didn't provide a link. The plastic pizza wheel is superior (faster) to the guitar pick but either will work. Be careful with the pick and keep going around till the seal is broken all around.

Techs use rolls of tape but if only doing one iMac, the tape kit is great. OWC sells kits, too.