rob53

Detnator said:

rob53 said:

This hub is like OWC's 4-port Thunderbolt hub. It also says it can drive two 4K displays and costs $20 less. The Sonnett hub will also have limitations when connecting too many devices that want to use as much of the TB bandwidth as possible. I've seen questions about using a hub like this to create a RAID using three NVMe external drives and software RAID. It might be fun to try but I wouldn't expect the full 5000Mb/s TB3 bandwidth. This hub will be used to connect multiple devices that don't require simultaneous use. 

I'd love to be proved wrong but I only have a 2020 M1 MBA to test with and it has Thunderbolt limitations.

I have two of the OWC hub you mentioned, and a number of high end NVMe drives in various enclosures, and I've tried to do exactly this.  Sadly, there are some limitations.

For one, I'm not exactly sure of the details, but I believe the 40Gb/s TB channel (in TB3 at least, and I believe this part is unchanged in TB4) is split into some specifically for data and the rest specifically for video, and neither gets the full 40. It's likely there's some part of that sentence that isn't quite right, but the upshot, as I understand it, is that the maximum SSD throughput you can get out of a single TB3 channel is about 2800MB/s or 2.8GB/s  (note: MBytes/GBytes, not Mbits/Gbits).

This 2800 is usually stated on TB drives and enclosures from companies who are honest with their marketing (while everyone else says misleading statements like "full 40Mb/s bandwidth"), and I would say it mostly agrees with my experience in practice... or at least that's the case under ideal conditions, though most conditions are short of ideal (eg. background processes doing stuff that chews up some of the bandwidth etc).

Based on those numbers I bought myself two OWC 4M2 TB3 enclosures and I get about 2200 MBps throughput on each of those, and when I stripe them all I get at most about 3500, usually not quite that much. That's the case on both my maxed out 2020 M1 13" MBP and my maxed out 2019 Intel 16" MBP.  And I've generally got similar performance out of other striped NVMe SSD configurations I've tried (eg. with some of the bus powered single drive enclosures).  When I had an iMac Pro I got better speeds out of the same configurations.  But despite trying various different configurations and setups, no setup has ever got me anywhere near the 5000MBps you'd expect/hope from a theoretically maxed out single 40Gbps TB channel, and in fact, I've never even got that much out of two channels striped.

Important to note that all this is per CHANNEL, not per port. The Intel Macs share two ports per channel, so the four port Intel MBPs and iMac Pro have two channels. The two port Intel 13" MBP and MBA have one TB channel. On all Apple Silicon Macs so far I believe it's one port per channel, which means the low end 13" M1 MBP and MBA have two channels, despite only two ports -- which is an upgrade over the 2-port Intel machines they replaced.  And on the new 2021 14" and 16" M1 Pro/Max MBP's, the three ports, although a downgrade in number of ports are a 50% upgrade in bandwidth over the previous 4-port (2-channel) 13" and 16" Intel MBPs.

That's a bit of a ramble, to include a lot of detail.  The point is it's my understanding that the maximum theoretical data (ie. SSD drive) throughput of any single thunderbolt channel is 2800MBytes/s.  And in practice it's generally significantly slower.  I believe there are some other overheads interfering with drive performance, which no doubt include background processes trying to do stuff among other things.  The other factor I've found (and this might be where the iMac Pro benefited most) is that these ports get very hot, and if allowed to get too hot will burn out the electronics, and they have built in throttling to slow them down if they get there.  Things like ice packs or keeping your Mac in a refrigerator might help with that... that's something I want to try one day.

So needless to say... unfortunately these hubs don't really improve speed because the bottleneck is the channel more than anything else.  Some drive enclosures are slower than the channel bottleneck, but the best these hubs will give us is bringing multiples of those enclosures, striped over one channel, up to similar speeds as the already fast enclosures can do. There might also be some benefit in spreading the heat around, although there's still the heat at the single host port, the management of which may or may not have improved in the newer MBPs.

I'm keen to get a new M1 Max MBP and see if that's the case, and how fast I can get drives striped across all three channels to go. I'll probably do a brand new clean install to minimize other overheads, and for theoretical/experimental interest I might try it in the fridge and see if that helps. 😉   I'll report back my findings when I can get my hands on one of those machines.