Comment by fenced_load
2 months ago
Mikrotik has a switch that can do 6x200g for ~$1300 and <150W.
https://www.bhphotovideo.com/c/product/1926851-REG/mikrotik_...
2 months ago
Mikrotik has a switch that can do 6x200g for ~$1300 and <150W.
https://www.bhphotovideo.com/c/product/1926851-REG/mikrotik_...
Wow, this switch (MikroTik CRS812) is scary good for the price point. A quick Google search fails to find any online vendors with stock. I guess it is very popular! Retail price will be <= 1300 USD.
I did some digging to find the switching chip: Marvell 98DX7335
Seems confirmed here: https://cdn.mikrotik.com/web-assets/product_files/CRS812-8DS...
And here: https://cdn.mikrotik.com/web-assets/product_files/CRS812-8DS...
From Marvell's specs: https://www.marvell.com/content/dam/marvell/en/public-collat...
Again, those are some wild numbers if I have the correct model. Normally, Mikrotik includes switching bandwidth in their own specs, but not in this case.
They are very popular and make quite good products, but as you noticed it can be tricky to find them in stock.
Besides stuff like this switch they've also produced pretty cool little micro-switches you can PoE and run as WLAN hotspots, e.g. to distance your mobile user device from some network you don't really trust, or more or less maliciously bridge a cable network through a wall because your access to the building is limited.
That switch appears to have 2x 400G ports, 2x 200G ports, 8x 50G ports, and a pair of 10G ports. So unless it allows bonding together the 50G ports (which the switch silicon probably supports at some level), it's not going to get you more than four machines connected at 200+ Gbps.
As with most 40+GbE ports, the 400Gbit ports can be split into 2x200Gbit ports with the use of special cables. So you can connect a total of 6 machines at 200Gbit.
Ah, good point. Though if splitter cables are an option, then it seems more likely that the 50G ports could be combined into a 200G cable. Marvell's product brief for that switch chip does say it's capable of operating as an 8x 200G or 4x 400G switch, but Mikrotik may need to do something on their end to enable that configuration.
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Breakout cables typically split to 4.
e.g. QSFP28 (100GbE) splits into 4x SFP28s (25GbE each), because QSFP28 is just 4 lanes of SFP28.
Same goes for QSFP112 (400GbE). Splits into SFP112s.
It’s OSFP that can be split in half, i.e. into QSFPs.
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Cool! So for marginally less in cost and power usage than the numbers I quoted, you can get 2 more machines than with the RDMA setup. And you’ve still not solved the thing that I called out as the most important drawback.
how significant is the latency hit?
The OP makes reference to this with a link to a GitHub repo that has some benchmarks. TCP over Thunderbolt compared to RDMA over Thunderbolt has roughly 7-10x higher latency, ~300us vs 30-50us. I would expect TCP over 200GbE to have similar latency to TCP over Thunderbolt.
Put another way, see the graphs in the OP where he points out that the old way of clustering performs worse the more machines you add? I’d expect that to happen with 200GbE also.
And with a switch, it would likely be even worse, since the hop to the switch adds additional latency that isn’t a factor in the TB5 setup.
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