iMac late 2015 with 3TB HDD but no Fusion?

[rin67630]

Hi I just have acquired an iMac late 2015 Retina:
Hardware Overview:
Model Identifier: iMac17,1 Processor Name: Intel Core i5 Processor Speed: 3,2 GHz
Number of Processors: 1 Total Number of Cores: 4 L2 Cache (per Core): 256 KB
L3 Cache: 6 MB Memory: 8 GB Boot ROM Version: 509.0.0.0.0
SMC Version (system): 2.33f12 Serial Number (system): DGKQX03BGQ18
Chipset Model: AMD Radeon R9 M390 PCIe Lane Width: x16 VRAM (Total): 2 GB


According to EveryMac this Model was either sold with 1 TB HDD or a 2TB fusion drive, or a 3TB fusion drive:

At the time of purchase, Apple offered a 2 TB "Fusion Drive" (which combines a 128 GB SSD and a 2 TB hard drive) for an extra US$200, a 3 TB "Fusion Drive" (which combines a 128 GB SSD and a 3 TB hard drive) for an extra US$300, a 256 GB SSD for an extra US$100, a 512 GB SSD for an extra US$400, or a 1 TB SSD for an extra US$900.

So, according to the size of the HDD and the graphic card M390, i should have the model with a fusion drive.

However only a plain HDD is reported.
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_HFS Mojave 3.0 TB disk0s2


Can it be that the SSD blade is defective and the iMac was "repaired" upon reinstalling on the HD only?

 

[kagharaht]

Did you download Mactracker? It shows that a 3TB HDD 7200 SATA can be configured with that model.

 

[rin67630]

Did you download Mactracker? It shows that a 3TB HDD 7200 SATA can be configured with that model.

Thank you, I yet trusted EveryMac.
So a stupid 3TB plain HDD can be configured. :-(

How are my chances to retrofit a blade SSD?
I would prefer not to take the iMac apart just to discover that the NVMe port is not populated.

I fact I don't want to build a fusion drive, but to have the OS and apps on the SSD and my data on the HFS+ HDD.
I have done it with other systems and it works very well even with Ventura.

 

[rin67630]

Today the 121GB blade did show up, but no way to initialize it.
So, clearly, defective SSD.

 

[rin67630]

So I did the repair: two hours screwing: I replaced the defective Fusion blade with a 121GB NVMe drive left from an upgrade of a Macbook air 2015.
Works like a charm: the 121GB is formatted APFS and holds the OS and the Apps. The 3TB HDD is formatted HFS+ and holds the user data and a time machine partition.

 

[Anonymous Freak]

If you really want it all to appear as a single drive, and have the OS handle dividing apps between SSD and HDD, you can manually create a Fusion Drive: https://www.lifewire.com/setting-up-fusion-drive-mac-2260165

 

[rin67630]

If you really want it all to appear as a single drive, and have the OS handle dividing apps between SSD and HDD, you can manually create a Fusion Drive: https://www.lifewire.com/setting-up-fusion-drive-mac-2260165

But I don't want that ! That was a really dumb idea from Apple.
It's ways faster to have the OS on the blade and the data on the HDD.
Additionally, APFS ist HD Disk jammer. It is MUCH better to have HDDs formtted HFS+

 

[Anonymous Freak]

It depends on how much you trust Apple’s algorithms. The whole point is that the OS decides what data belongs where. OS+apps get put on the SSD 99% of the time, and “user data” stays on the spinny-rust 99% of the time. But you may run into cases where you have high-data-usage apps where a lot of the data is rarely used (Microsoft Office) so when it realizes that, it will move that data over to the HDD, freeing up SSD space. And if you have some “user data” that gets loaded *a lot*, it will move that to the SSD. It’s a constant balance of what data goes where.

And you can make a Fusion Drive HFS+. (In fact, in the first few OSes that supported APFS, Fusion drives *COULDN’T* be APFS, they HAD to stay HFS+.)

 

[ignatius345]

It depends on how much you trust Apple’s algorithms. The whole point is that the OS decides what data belongs where. OS+apps get put on the SSD 99% of the time, and “user data” stays on the spinny-rust 99% of the time. But you may run into cases where you have high-data-usage apps where a lot of the data is rarely used (Microsoft Office) so when it realizes that, it will move that data over to the HDD, freeing up SSD space. And if you have some “user data” that gets loaded *a lot*, it will move that to the SSD. It’s a constant balance of what data goes where.

And you can make a Fusion Drive HFS+. (In fact, in the first few OSes that supported APFS, Fusion drives *COULDN’T* be APFS, they HAD to stay HFS+.)

Fusion Drives were an amazing idea back when SSDs were horribly expensive. I did a DIY Fusion Drive back in like 2014 or so when I crammed a 128 GB SSD into my Mini alongside the HDD it came with. I used some Terminal commands I read about and bam, the two drives acted like one much faster drive at a time when a 1 TB SSD would've cost me like a month's rent.

The hitch in it, though, is that the SSD part gets absolutely hammered with read/write cycles with all that data moving back and forth between the two -- especially the tiny SSDs Apple was using (as small as 32 GB if I'm remembering right). The Fusion Drive in my iMac 5K eventually bit the dust, and it was the SSD that was going bad because it was just plain worn out.

What I'm unclear on is why the OP, when he presumably had his iMac opened up, didn't just replace that SATA HDD with a SATA SSD. Opening those things up is a real PITA and I'd sure as hell take that opportunity to put in an SSD while I could. But whatever!

 

[rin67630]

It depends on how much you trust Apple’s algorithms. The whole point is that the OS decides what data belongs where. OS+apps get put on the SSD 99% of the time, and “user data” stays on the spinny-rust 99% of the time.

...

And you can make a Fusion Drive HFS+. (In fact, in the first few OSes that supported APFS, Fusion drives *COULDN’T* be APFS, they HAD to stay HFS+.)

The point is that you cannot make a fusion drive APFS (required by the newer OSes) and HFS+ at the same time.
APFS is a HD drive killer.
So if you want to go beyond Mojave you end up with a crappy APFS fusion drive that will fragment your HD to death.

When you work with split drives, you can get the OS on APFS and the HD on HFS+ getting the best of both technologies.
That is faster, copes with more recent OSes and is safer: In fact I think the FD writes the inodes references to the SSD and leaves the user data on the HD to avoid head moves. When the SSD fails, the HD without the inodes references is useless, that's why a FD loses all data if the ssd blade fails.
Last, but not least: the OS data on the NVMe is mostly read, not permanently written like when used as a Fusion drive.

 

[rin67630]

What I'm unclear on is why the OP, when he presumably had his iMac opened up, didn't just replace that SATA HDD with a SATA SSD. Opening those things up is a real PITA and I'd sure as hell take that opportunity to put in an SSD while I could. But whatever!

The SSD of a 2015 iMac is NVMe, which is 4 times faster than SATA. So running the OS from MVMe is better performance.
OK I could have replaced the 3TB HDD with a SATA SSD too, but that's adding cost for nothing.
Used only for data a HD is fairly fast. No need to add cost.