Can all Macs, irrespective of age, benefit from fast NVMe SSD (external) with 3,500 MB/s speed?

[minvoyager]

I aim to get an external SSD drives for my iMac late 2015 Retina 27" 3.2 GHz i5. The SSD will be housed in an external case attached with USB 3.0 cable.

My main concern is Read Speed.

Given that there are older 2.5 inch SATA SSD's with a read speed of around 500 MB/s, and then there are MVMe SSD's with read speeds of over 3,500 MB/s - I wonder if any Mac can benefit from these very fast SSD's with 3,500 MB/s read speeds. Or is it the case that only newer Macs with certain features can take advantage of these extremely fast 3,500 MB/s SSD's?

If it requires a more recent Mac, newer than my 2015 iMac Retina, then it'd be a waste to spend extra of these fast 3,000 MB/s SSD's for my 2015 iMac.

 

[Juicy Box]

Just based on the comparison between an external SATA and external NVMe, I think your question if any Mac can benefit depends totally on what is being done on the Mac.

If one is using their Mac to catch up on the latest MR news, while checking the weather, and streaming Netflix, any benefit from the much faster NVMe will probably hardly ever be realized.

For your specific case, using NVMe with USB3 will most likely not be any different than using SATA with USB3.

To get the most out of NVMe, I would use Thunderbolt. I have not done it, but I have read that using Apple's TB3>TB2 adapter allows for TB3 devices on older TB1 and TB2. There are conflicting posts about if it works for bus-powered devices though. Still, this would be the best way for you to take advantage of an external NVMe.

With Thunderbolt 2, you could see speeds up to 2,500 MBps, but with USB3, it would be limited to 625 MBps.

 

[Stephen.R]

So there's several things at play here: (and keep in mind: the capitalisation of the 'b' matters: lower case means bits, upper case means bytes. 8 bits = 1 byte)

USB3 (limited to 5 Gbps, so theoretically 625 MB/s, real-world will be less, maybe 550 MB/s)
SATA3 (limited to 6Gbps, so theoretically 750MB/s, real world will depend on the underlying storage media, most SATA SSD's top out around 560 MB/s)

There's also NVMe and Thunderbolt (both of which make use of PCIe channels for data transfer) but that's getting a lot more expensive and will need an adapter for a Thunderbolt2 equipped Mac like yours.


So, to answer your question: yes, a 3500MB/s NVMe drive is a waste of money if it's just connected via USB3.0. Almost any NVMe drive is going to be "wasting money" if it's connected via USB3.0: When I wanted a cheap one to pair with a USB3.1Gen2 (so, 10Gbps) M2 case, even the cheapest/slowest ones I found had read and write speeds around 1GB/s.


The good news for you, is that USB3.0/SATA external SSD's are very common, so there's plenty to choose from, and it'll definitely be a speed boost compared to a mechanical drive.

 

[joevt]

With Thunderbolt 2, you could see speeds up to 2,500 MBps, but with USB3, it would be limited to 625 MBps

Thunderbolt 2 is 20 Gbps = 2500 MB/s but that's not including overhead. Thunderbolt 2 controllers are connected using PCIe 2.0 x4 (5 GT/s/lane x 4 lanes x 8b/10b) = 16 Gbps = 2000 MB/s. But with overhead (not all bytes are used for data), it's more like 1600 MB/s. The rest of the 20 Gbps can be used by DisplayPort.

Thunderbolt 3 is limited to 22 Gbps for PCIe traffic. That's 2750 MB/s. The rest of the 40 Gbps can be used by DisplayPort.

8b/10b means there are 10 bits transmitted for every byte of data. Thunderbolt uses 64b/66b but that is already included in the 10/20/40 Gbps numbers (bits on the wire is actually 10.3125/20.625/41.25 Gbps).

USB3 (limited to 5 Gbps, so theoretically 625 MB/s, real-world will be less, maybe 550 MB/s)

USB 3.0 = 5 Gbps * 8b/10b = 500 MB/s (Real-world 450 MB/s)
USB 3.1 gen 2 = 10 Gbps * 128b/132b = 9.697 Gbps = 1212.12 MB/s (real world 1000 MB/s). Some USB 3.1 gen 2 controllers are limited by PCIe 2.0 x2 = 5GT/s * 2 * 8b/10b = 8 Gbps = 1000 MB/s (real-world 760 MB/s) or PCIe 3.0 x1 = 8 GT/s * 128b/130b = 7.877 Gbps = 984.6 MB/s (real-world 750 MB/s).

SATA3 (limited to 6Gbps, so theoretically 750MB/s, real world will depend on the underlying storage media, most SATA SSD's top out around 560 MB/s)

SATA3 = 6 Gbps * 8b/10b = 600 MB/s (real world 560 MB/s)

There's also NVMe and Thunderbolt (both of which make use of PCIe channels for data transfer) but that's getting a lot more expensive and will need an adapter for a Thunderbolt2 equipped Mac like yours.

NVMe = PCIe 3.0 x4 = 8 GT/s * 4 * 128b/130b = 31.5 Gbps = 3938 MB/s (real world 3500 MB/s).

(All real-world numbers are approximate guesses)

 

[Juicy Box]

Thunderbolt 2 is 20 Gbps = 2500 MB/s but that's not including overhead. Thunderbolt 2 controllers are connected using PCIe 2.0 x4 (5 GT/s/lane x 4 lanes x 8b/10b) = 16 Gbps = 2000 MB/s. But with overhead (not all bytes are used for data), it's more like 1600 MB/s. The rest of the 20 Gbps can be used by DisplayPort.

Thunderbolt 3 is limited to 22 Gbps for PCIe traffic. That's 2750 MB/s. The rest of the 40 Gbps can be used by DisplayPort.

8b/10b means there are 10 bits transmitted for every byte of data. Thunderbolt uses 64b/66b but that is already included in the 10/20/40 Gbps numbers (bits on the wire is actually 10.3125/20.625/41.25 Gbps).


USB 3.0 = 5 Gbps * 8b/10b = 500 MB/s (Real-world 450 MB/s)
USB 3.1 gen 2 = 10 Gbps * 128b/132b = 9.697 Gbps = 1212.12 MB/s (real world 1000 MB/s). Some USB 3.1 gen 2 controllers are limited by PCIe 2.0 x2 = 5GT/s * 2 * 8b/10b = 8 Gbps = 1000 MB/s (real-world 760 MB/s) or PCIe 3.0 x1 = 8 GT/s * 128b/130b = 7.877 Gbps = 984.6 MB/s (real-world 750 MB/s).


SATA3 = 6 Gbps * 8b/10b = 600 MB/s (real world 560 MB/s)


NVMe = PCIe 3.0 x4 = 8 GT/s * 4 * 128b/130b = 31.5 Gbps = 3938 MB/s (real world 3500 MB/s).

(All real-world numbers are approximate guesses)

All the numbers I posted are obviously theoretical max from the bus. I was going to post real world numbers as I have done in other threads with similar questions, but with limited time I passed on it.

Either way, I think it answers the OP's question asking if the extra speed is answered pretty well.

To the OP: Another thought about NVMe, the prices are starting to come down, while they are not as cheap as SATA SSDs, the price gap is starting to close.

While you wouldn't see the benefits of using the much faster NVMe compared to SATA over USB3, it might be worth considering if you think you may upgrade your computer anytime soon for future proofing.

 

[joevt]

All the numbers I posted are obviously theoretical max from the bus.

That's fine. Except theoretical max numbers should at least take into consideration encoding overhead (8b/10b in the case of SATA and USB 3.0). I've never seen anyone say SATA has a max of 750 MB/s before. That's because a byte takes 10 bits to transmit.

For External SSD, what I did was choose the cheapest NVMe that can do at least 1000 MB/s and put it in an inexpensive USB-C to NVMe adapter to get max USB 3.1 gen 2 speed (10 Gbps). The 2TB Intel 660p is good for that. USB is more compatible and much cheaper than Thunderbolt.

 

[Fishrrman]

OP wrote:
"If it requires a more recent Mac, newer than my 2015 iMac Retina, then it'd be a waste to spend extra of these fast 3,000 MB/s SSD's for my 2015 iMac."

You've answered your own question with the comment above.

A 2015 iMac has USB3.
The fastest, easiest, cheapest way to improve boot/run times would be to buy a USB3 SSD (such as the Samsung t5, but that's not the only one), and set that up to be the new boot drive.
That will yield read speeds of 430mbps and writes in the 350-375 range (or a little higher).

The 2015 can't "use" the extra speed of the super-fast nvme drives (in external enclosures, such as the Samsung X5) that are now appearing. The in/out capabilities aren't fast enough for the drive.

But you couldn't use the X5 anyway, as it requires a USBc/thunderbolt3 connection (to the Mac). The thunderbolt2 to thunderbolt3 adapter won't work, due to "bus power issues".

I'd get a USB3 SSD and be done with it.

 

[joevt]

A 2015 iMac has USB3.

USB 3.0 is 5 Gbps. Add USB 3.1 Gen 2 (10 Gbps) with a Thunderbolt 3 dock and Apple's Thunderbolt 3 to Thunderbolt 2 adapter.

The fastest, easiest, cheapest way to improve boot/run times would be to buy a USB3 SSD (such as the Samsung t5, but that's not the only one), and set that up to be the new boot drive.
That will yield read speeds of 430mbps and writes in the 350-375 range (or a little higher).

You mean 430 MBps (capital B for bytes). The T5 supports USB 3.1 Gen 2, so you could get slightly faster sequential reads with the Thunderbolt 3 dock idea (up to 540 MB/s since the T5 uses a SATA 6 Gbps drive).

The 2015 can't "use" the extra speed of the super-fast nvme drives (in external enclosures, such as the Samsung X5) that are now appearing. The in/out capabilities aren't fast enough for the drive.

The 2015 could at least get 1600 MB/s using Thunderbolt 2. That's 3 times faster than SATA.

But you couldn't use the X5 anyway, as it requires a USBc/thunderbolt3 connection (to the Mac). The thunderbolt2 to thunderbolt3 adapter won't work, due to "bus power issues".

An intermediate Thunderbolt 3 device such as a Thunderbolt 3 dock can provide enough power if the Apple Thunderbolt 3 to Thunderbolt 2 adapter cannot.

I'd get a USB3 SSD and be done with it.

Yup.