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Late 2012, 27”, bandwidth of pci-e

S

sergiobaschi

macrumors regular
Original poster
Nov 30, 2012
199
6
Gothenburg, Sweden
I have an iMac 2012 with 1.1 TB Fusion Drive. Does anyone know the bandwidth of the pci-e connection in which the SSD is connected?

I’m looking for upgrading options and it would be nice to not be SATA-limited...
 
sergiobaschi said:
I have an iMac 2012 with 1.1 TB Fusion Drive. Does anyone know the bandwidth of the pci-e connection in which the SSD is connected?

I’m looking for upgrading options and it would be nice to not be SATA-limited...
Click to expand...


Sure the SSD in the 2012 model is connected via PCIe? I thought they moved to PCIe in 2013... Oh well.
Regardless, I know the PCIe lanes in the iMac are PCIe 3.0. I would assume the SSD is using 4 lanes, but it may only be using 2 lanes

If it's x2, it's 1.970MB/s theoretical.
If it's x4, it's 3.940MB/s theoretical.

You can also use Thunderbolt - I believe your iMac has Thunderbolt 2, yes? If so that'll give you 4 lanes of PCIe 2.0 over the Thunderbolt port, which is equivalent to PCIe 3.0 x4. Then there's a bit of overhead added for Thunderbolt, but it's not that much.
 
SSD in Late 2012 model is connected to SATA 3.0 lines on the same bus as hard drive, probably good for Fusion implementation
 
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sergiobaschi said:
I have an iMac 2012 with 1.1 TB Fusion Drive. Does anyone know the bandwidth of the pci-e connection in which the SSD is connected?

I’m looking for upgrading options and it would be nice to not be SATA-limited...
Click to expand...

So, just to be clear, Fusion Drive isn't a single drive. It's 2 drives, one SSD and a traditional form factor SATA HDD, with a software volume manager that manages the placement of data on SSD vs. HDD. Your computer has a 1TB traditional HDD mated to a 128GB SATA SSD (blade style), mated via software volume manager called Core Storage.

So, if you remain with Fusion Drive, you will always have SATA limitations on the HDD portion. And as further noted, your 2012 iMac (I own one too!) uses SATA for the internal SSD as well, it is 6Gbit connected. Later Macs moved to PCIe SSDs (SATA protocol, not NVMe) and then even later went to full NVMe (PCIe connected but NVMe instead of SATA protocol)

Your upgrade options are as follows (simplifying it), choose one:

1) Find an upgrade SSD for the Fusion Drive, something much bigger than the 128GB that is in there now. Then use it as a non-fused boot drive. Or fuse it again with the 1TB drive and you'll have a larger Fusion Drive, I have fused 512GB SSDs with 1TB HDDs for a 1.5TB do-it-yourself Fusion Drive that is very fast almost all the time.

2) Replace the 1TB HDD with an SSD, say a 2TB Samsung unit. Use it independently of the 128GB SSD. Note that you'll want to get a kit that emulates the thermal temperture probe that Apple HDDs have otherwise your fan speeds will go up (a little or a lot, depending).

3) Leave the Fusion Drive as-is, and boot from a Thunderbolt connected SSD (or USB-3, but my preference is Thunderbolt to get guaranteed access to TRIM on a TRIM-capable SSD, although you can get that through USB-3 with the proper enclosure if you do your homework).

#3 is how i run my 2012 iMac. I boot from an external 512GB SSD, and I use my Fusion Drive (reformatted) for data. I also upgraded the 1TB HDD in my Fusion Drive to 2TB, using the instructions and parts kit offered by iFixit.com.
 
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OP:
Fastest, easiest, cheapest, safest way to upgrade the drive for more performance is to buy an EXTERNAL USB3 SSD, plug it in, and set it up to become your external boot drive.

No risk of breaking anything inside this way.
If you get something like a Samsung t5, you should see read speeds around 430mbps and writes around 350mbps.
 
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