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Model A1419 / EMC 3070 / Mid 2017 / 3.4, 3.5 or 3.8 GHz Core i5 or 4.2 GHz Core i7 Kaby Lake Processor (ID iMac18,3) / Retina 5K display. Refer to the older iMac Intel 27" Retina 5K Display (Late 2014 & 2015) guides as the system is very similar.

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Can the new 27" iMac Retina 5K display support two SSD's?

I want to put in two SSD's in a 27" iMac Retina 5K (mid 2017)?

I understand that such iMac has two different ports for two different disks inside (eg., one SSD or one Fusion drive from Apple).


1. Is it possible to install this disk inside to boot the iMac?

Samsung 960 PRO Series - 2TB PCIe NVMe - M.2 Internal SSD (MZ-V6P2T0BW)

Sequential R/W (read/write) speeds up to 3,500/2,100 MB/s and random R/W speeds up to 440/360K IOPS, respectively.

2. Is it possible to have two SSD at the same time inside the iMac?

For instance, the one SSD from Apple (or the one above, if possible) and other like this (now 2TB, soon 4TB)?

Samsung 850 PRO - 2TB - 2.5-Inch SATA III Internal SSD (MZ-7KE2T0BW)

Sequential Read/Write Performance: Up to 550MB/s and 520MB/s, respectively. Random Read/Write IOPS Performance: Up to 100K and 90K, respectively.


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Don't buy the Fusion Drive model if you want to reconfigure it with dual SSD's


Thanks. Why? Can the new 27" iMac Retina 5K display support two SSD?


The Fusion Drive is not what you think!

Simply put it uses both drive interfaces each supporting a drive (HDD & SSD) then using the OS to fuse the two drives into a logical fusion drive. At which point you won't have any spare ports! It is not a special physical drive.

Here's a good write up: 5 Things to Know About the Apple Fusion Drive


Just to be clear buying a SSD only model then adding in your own SSD is possible! So Yes you can build a dual SSD system as I outlined below. I don't recommend doing it as you will loose your warranty support!

Frankly, an external RAID'ed SSD setup will offer much faster performance than the SATA SSD! As an example we use OWC ThunderBay 4 mini with SSDs we get about 2k MB/s sustained using Thunderbolt 2!


Did you read what I posted below?

Again No on the 960 PRO! It won't work.You need to use the Apple SSD blade NVMe SSD and if you want a second SSD use the 850 EVO SATA drive don't use the 850 PRO SATA drive not worth the extra cost!


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Peter you won't be able to use the Samsung 960 M.2 NVMe SSD. Apple uses a custom PCIe NVMe interface. Besides, the Apple 1 TB & 2 TB units are faster than Samsung's!

You also appear to be looking at the Samsung Pro Series SSD's. Unless you are setting up a dedicated server there is little benefit going to the more expensive Pro line, stick with the EVO line.

  • FYI - I support over 300 MacBook Pro's which more than 2/3rds have Samsung 850 EVO's. I think we have only replaced one SSD in over three years of use!

As for installing a second SSD, Yes! That can be done as well. But lets first make sure you get the correct model here. You'll want to use the custom configuration selecting the SSD only option with the either the 3.8 GHz or the 4.2 GHz models selecting either the 1TB or 2TB option. Then you'll need to order a SATA HD cable, adapter frame to hold your 2.5" SSD in the 3.5" drive bay and lastly the in-line thermal sensor:

I would just stick with the Samsung 850 EVO SSD Vs the Pro model.

Two last points:

Opening your system will void the warranty, besides the newer 'Thin Series iMac's are a bear to open if you don't use the proper tools and techniques as outlined in the IFIXIT guides. It's quite easy to damage the display which would be a very expensive Opps!

Frankly, I would recommend you hold off on adding the second drive until the warranty period has expired. Instead, I would recommend going with an external Thunderbolt RAID'ed SSD unit as a better direction it will be faster than the SATA internal interface! And then use it for your backup drive.

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Thanks. I thought Samsung 960 PRO with sequential R/W (read/write) speeds up to 3,500/2,100 MB/s and random R/W speeds up to 440/360K IOPS, respectively was faster than Apple 2TB SSD which I think has 2,3/2,0 GB/s sequential R/W, respectivamente. Could the former be used in the iMac using an adapter?

On the other hand, could the Samsung 850 EVO 4TB (note the large capacity) be used besides the Apple SSD 2TB inside such iMac?


You found the older Disk Test report! You are referencing the older PCIe x2 SSD not the newer PCIe x4 which is faster. I can't put my hands on the bigger SSD config report right now. Trust me! The Apple larger SSD is faster than the Samsung SSD.

The answer is still no you can't fit the Samsung M.2 SSD within the custom Apple PCIe slot with any adapter. Still a square peg round hole problem!


"The Apple larger SSD is faster than the Samsung SSD".

Wow, that is great news indeed!

On the other hand, I guess that the impossibility to use Samsung 960 PRO on the 27" iMac Retina 5K display is because the lack of Mac drivers for it. Right?


Why do you what to put in a Samsung M.2 SSD into this system? Is there some reason Apples SSD is so bad in your mind?

You do realize Samsung makes the custom SSD for Apple under contract.

Lastly, using an adapter does not mean the performance of the device will be the same Vs not using an adapter.

We did a bit of testing of some SSD's with M.2 to Apple adapter with MacBook Pro's awhile ago and I can tell you it was not good.

First we tested using three different SATAe (AHCI) blade SSD's in SATAe based systems they worked but the performance was not as good as Apple's SSD's. We then tested them within PCIe x2 based systems this is where there was problems as the newer MacBook Pro's couldn't support the older SATAe drives (lots of CRC errors).

We tried a few at that time PCIe SSD's and they too did not work well either (we suspect they were running in compatibility mode (AHCI). We have not tested any of the newer PCIe x4 M.2 SSD's now on the market. But others have and they just don't work at all.

Basically, force fitting a M.2 SSD into a newer Mac (either MacBook Pro or iMac) is a pointless exercise.


Dan, I am gladly amazed how great your support is. Second to none! Many thanks indeed!

Maybe the incompatibilities that you mention are due to the lack of true Mac drivers for such SSD.

I wanted the Samsung 960 PRO in the 27" iMac Retina 5K (mid 2017) because I thought it was better (faster) than the one from Apple. Anyway, what are the sequential and random read/write speeds of the Apple 2TB PCIe SSD on such iMac? You said that it was faster than the Samsung 960 PRO.


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Surprising results for 27" iMac Retina 5K (mid 2017):

TESTED: 2017 iMac 5K SSD Speed vs 2015 iMac 5K (Surprising Finding)

Thus the 2017 iMac 5K is substantially slower for everyday tasks that involve intensive I/O with smaller reads, in spite of the 40% greater speed for large reads.


2017 iMac 5K: Flash Drive (SSD)

2015 iMac 5K: writes at 1520 MiB/sec and reads at 2075 MiB/sec

2017 iMac 5K: writes at 2102 MiB/sec and reads at 2915 MiB/sec.


That is less read speed than Samsung 960 PRO with sequential R/W (read/write) speeds up to 3,500/2,100 MB/s and random R/W speeds up to 440/360K IOPS, respectively.

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Peter you need to read the fine print!

This is likely the smaller SSD used in the Fusion Drive! Which makes total sense why the small block transfers are not as good.

Read up on the difference between small and large sized SSD's then look for a large real life SSD performance test. Even still it shows good performance with DiskTests mixed sized data test.

FYI: Opt For the Larger SSD Capacity to Also Get a Speed Boost


Thanks, They say "Both machines utilized the Apple 1TB SSD" on "2017 iMac 5K: Flash Drive (SSD)" article. So, it does not seem to be the Apple Fusion, but the full Apple SSD (albeit the 1TB instead of 2TB).

On the other hand, I have chosen the 27" iMac Retina 5K (mid 2017) with Apple 2TB PCIe SSD inside (I would have chosen a larger one if available).

BTW, what are the sequential and random read/write speeds of such Apple SSD? You said that it was faster than the Samsung 960 PRO.


Regarding Peter Gamble's first posting... That connector on the wee-tiny proprietary PCIeSSD on the iMac 2017 looks like the one on my MacBook Air 2015, which I managed to swap out with a larger Toshiba KXG50ZNV512G. It works great - zero problems, even with sleep. YES. TRUE. It is for a MacBook Air. And Peter is talking about an iMac. However...

... after a bit of Googling, the connectors for the wee-tiny 28GB PCIeSSD looks the same as the connector for my Apple original SSD that came out of my MacBook Air. I got the new Toshiba to fit using a SINTECH adapter, which, again, to date has shown no problems, even in terms of speed.

Now, I'm not as knowledgable as most you guys here but I'm handy with tools and my hands. Wouldn't that same SINTECH work for Peter Gamble and his desired Samsung 960?

OR is what people are saying Apple has done some other things with their physical 28GB PCIeSSD like additional controller/chips that the 960 doesn't have?


PS., David Palmer, Great idea! Love it. Practical man you are.


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Hope I can be helpful here. I own a 2015 iMac (model17.1) with which I replaced the blade drive and added an internal 2TB SSD. I bought the iMac with a 256GB SSD, which was a mistake. I thought I could use the Thunderbolt bus for more space but there is something wonky with the bus… at least in the 2015 model. The slightest wiggle to the cable will make the drive dismount.

I recommend buying the largest blade SSD you can afford. I ended up spending another $1000+ and many tedious hours upgrading to a 1TB blade drive.

My answers to your questions:

1, It will have an open port but NOT a SATA cable. Yes you will have to take apart the entire computer. I found it to be not that difficult, but I’ve been a builder for decades.

This is the way to go IMO. You will have an open port and brackets for mounting a 3.5” traditional spinning hard drive. You will need to buy a cable and an adapter for an SSD. The NewerTech product is great. Don’t skimp here.

The cable will cost you $45 or so… again, don’t skimp and find an Apple cable. It’s a long cable that wraps from the back to the front of the machine.

  1. This is a judgement call. I experienced sleep problems with what was supposed to be an Apple part (Thankfully, the Mojave update solved this). You are faced with a dilemma here… if you want internal storage (a must in my mind) you will need to dissect your new iMac… not a difficult thing if you take time and care. My experience says buy the largest internal SSD you can afford and then prepare for a challenge in adding additional internal storage. You will need a bracket and a cable… about $50 together. And a good day dedicated to dissecting your new machine. After all this work, don’t skimp on the internal drive… go with 2TB or more.

It’s worth it.

p.s. Strange comment section programming here

I've maintained an entire major university of computers including a mainframe running Unix not Linux (not that impressive since nobody had laptops in that day and routers were hideously expensive). I worked on a NeXT box at the time (which I had to hack into bc the previous guy quit). I’m a silverback.

My main advice to anyone is to keep things as simple and OEM as possible. Complexity is your enemy… keep it simple.

Sorry this message was meant to come after the next messages... strange comment section programming...

Alex, I highly recommend AVOIDING external drives as system disks. They're fine for data, but I would not use them for the system. TB3 is crazy fast and theoretically close to internal speeds, but there's always an overhead with any external bus, and you're increasing the number of fail points by using an external drive.

As you probably already know, Apple uses a proprietary blade pinout in their NVMe SSDs. OEM blade SSDs for the iMac are rare and accordingly expensive. And of course not under warrantee. I ended up paying more for a compatible 1TB blade drive than I would have if I had bought it preinstalled from Apple. And the drive created sleep problems that were thankfully cured with the Mojave system. Bottom line is I regretted trying to save money on the internal drive, although everything is working fine now. My advice would be to go ahead and spec the largest internal SSD you can afford, but not the 256GB. It filled quickly for me, and I had to resort to all sorts of stupid tricks such as symbolic links (like an alias but system-level) to use an external SSD for apps and the home folder. It made my system more complex and fragile and frankly a headache.

I eventually bought the 1TB Polaris blade SSD for about $300 more than I would have paid if I had specced a 1TB internal SSD at the Apple store. And the original 256GB blade is sitting in a drawer because nobody has made a decent external enclosure for the Apple pinout (last time I checked OWC was the only choice and their solution didn't work).

So go ahead and spec the largest internal SSD you can afford – I personally recommend 1TB, but I create illustrations and animations for a living now so HD space is always at a premium.If you go for a fusion drive you should know that it is basically a RAID 0 arrangement and as such it's not as secure or as fast as a single blade drive. Fusion drives are basically a strange cul-de-sac in the evolution of computer media; in other words, a kludge. I would recommend against it. If you do go that way you will have the cable needed for the additional SSD and will only need an SSD adapter. But I would not go that way. You will be wasting money and warranty.

The cable you picked looks right to me... I would get a guarantee from the seller that this will work. I personally went on eBay and found a genuine used Apple part. It cost more (like $35 or something) but to buy anything other than Apple parts is false economy in the scheme of things. The single most important thing with your computer is your data: don't skimp on your data!

Soooo final advice: buy the largest internal SSD you can afford 512GB or above. Buy the Newertech adapter. Buy an original Apple cable. Buy a Samsung SSD (I bought the Pro version but I read that there is little difference in terms of service hours or reliability. I always go pro with data though). Buy an Olfa knife and extrude it just under 1/4" to cut the tape – no need for those wheel things. Just go gently (the Olfa cutter will be a valuable tool afterward). Buy a yoga block to stick under the screen to keep it tilted up, or maybe even just fold some cardboard. Buy a tape kit. Do the operation in a well-lit generous space, like a kitchen table. Cover the table with a bedspread or some other thick cloth that will catch and keep those tiny screws.

And enjoy the process and the engineering! I think working on the iMac is pretty fun and not too stressful if you take it easy and enjoy it – you'll be gutting it pretty much completely which I'm sure you'll enjoy ;D. Oh make sure you have a Torx bit that is large-ish, like T25 Im thinking. There's one Torx bolt along the way that is larger than most computer kits include. iFixIt has the spec (and the best guide of course).

Best to you my friend!

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@bigh thanks so much for your reply. I’m leaning towards the apple blade SSD bc of compatibility issues, but i’m still considering external or upgrading the blade.

The main issue I have with external storage is it seems to be a lot slower read/write than internal. Do you know of any external storage that has comparable speeds via TB3?

My thought is if i’m already opening it up, I might as well squeeze out all the performance i can. If I did this, I’d obviously get the cheapest Fusion option and personally upgrade the rest. Can I ask what your main issues with replacing the blade drive were since you mentioned it was not the actual dissembly? I have a friend who has gotten inside a few iMacs and I have built a hackintosh, so I am fairly confident we will be able to successfully get in and out.

Finally, does this look like the correct SATA/power cable if I decide to go with the standalone Apple SSD?



Hey I just did what you're considering on my 2015 27" iMac, so I can definitely say it's possible. I would recommend getting a 1TB built-in SSD to start with – Apple charges less than any you can find on the street.

The internal SSD for the 2017 models is very specific, so the one you're asking about won't work – the pins are in the wrong arrangement. Apple increased the datapath by 50% so it's incredibly fast (2.7GB/sec read and 2.1GB/sec write). You'll need a genuine Apple "SSPOLARIS" SSD– the part number is 655-1995 so you can google this. 1TB is $900-$950.

The second (2TB) SSD will work fine, and should give you read/write specs around 500MB/sec The iMac will have the brackets for an internal HDD, but you will need an adapter like the NewerTech to mount it securely. You DO NOT need the OWC thermal adapter thing. You'll also need HDD pins to hold the adapter in place, a SATA cable (years 2013+ should work), and a tape kit for the screen – all available on eBay.

I personally like having an internal extra SSD, so I think you're smart to do this. Don't be too influenced by theoretical bandwidths... reality is almost always less, and usually much less. And the convenience of an internal is something I personally like (I currently use about 6 external 2TB SSDs and 24 external HDDs in a variety of interfaces and RAID configurations, FWIW).

Here's a real-world example: on my iMac the internal SATA is 6 GBbps and the Thunderbolt2 bus is 20Gbps. So an external Thunderbolt2 SSD should be 3x the speed, right? Or at least faster anyway? Well, the exact same Samsung Pro 850 on internal SATA tests out at 520/490MB r/w, but while on external Thunderbolt2 (G-Drive enclosure) tests at 390/360 Gbps. Any external bus will take a toll on data rates due to the interface.

You'll need a RAID to get faster speeds, and RAID devices are expensive, complex, and often noisy. I've done it for more than 20 years, and now avoid it except for data protection and long-term storage.


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I feel like mentioning a few Fallacies:

  • Appeal to Authority
  • Argument from ignorance

There's a 47 page thread on getting the 960 EVO (in some cases the PRO) WORKING in Late 2013 MacBook Pro retina

I've actually had difficulty doing it my self...

But, I believe France is a real place despite never having been there. And people claiming the M.2 PCI drives work? Aren't faking a thread to waste time.

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I don't doubt people have gotten to work in a MacBook Pro, I have! But, thats not the same as an iMac! And different systems used different drives! Apple wasn't siting still either! So you do need to research things very thoroughly! Review this reference: The Ultimate Guide to Apple’s Proprietary SSDs

But getting to work is not the same as getting a reliable drive! Think of it this way you walk across a old bridge so its safe! Now you drive the car across, oops into the river you go! Thats the difference here!

A light weight test is not the same as a full blown test and even that has its limits without digging into the driver level to see if the drive has a a lot of CRC error's.

I wouldn't chance it as these are not well made adapter frames!


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Hey Guys, Dan mentioned a thunderbolt raid drive… I already have a 1tb SSD from crucial for my imac5k 2017 18,3 but too chicken to install it. For obvious reasons explained by dan in his previous post. Would the OWC external dock work to boot from or am I way off? Here’s what I’m talking about… https://eshop.macsales.com/item/OWC/TB2U...

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Hi Jeffrey. I think Thunderbolt 3 (aka USB 3.1 tweaked) is finally stable and fast enough for an external system drive. But I would never recommend an external drive as a system drive. To do so will introduce fail points, and render your system vulnerable.

You have a 1TB SSD... is it a blade drive or a boxed drive? Either would be preferential to an external drive IMO. Don't worry about opening your iMac... it's not nearly as bad as an iPhone or iPad. It's very do-able. Just take your time and use a big space... You'll need room to lay out all the parts as you take them off. But it's not difficult and fairly straightforward. Kind of fun if you have experience with building or modifying. I would rate it a 4 out of 10 in difficulty. Not too bad.

What is your stock HD?


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