My questions about CX4's are:
The thought process motivating this is that I've come to learn that macOS is finally shipping with an mlx5 driver so I need CX4 or better to get out of the box support on macOS, so the idea is to get hardware that will let that point to point operation just work, but I'm also wondering what it would give me in the way of options in the future when SFP28/QSFP28 based infrastructure like switches become affordable. If an option exists where I can have the best of both worlds it would be worth paying a bit more for that I think.
USUALLY it makes the most sense to get the cheapest compatible thing. In this case that would be a $70 MCX413 that is not capable of 50Gb, which saves a few bucks. However, once I move to SFP28 infrastructure such a card will be at a disadvantage compared to their 50 and 100Gb brethren. So it's also reasonable to perhaps spring for a MCX415A-CCAT to get 100Gbit capability which will allow it not to become obsolete quite so early.
- Can the cheaper CX4 Lx cards e.g. MCX4131A-GCAT 50Gbit cards operate at 40Gbit when connected directly to ConnectX-3 QSFP 40Gbit NICs (of which I already own 3 or 4)? The CX4 Lx product brief seems to indicate so.
- I found that CX4 non-Lx cards have BCAT and GCAT models which support 40/56GbE or 50GbE, and both are QSFP28. I'd like to know a bit more about what that means since the CX4 product brief didn't seem to clarify.
- Would the 50GbE models (e.g. MCX414A-GCAT) not support 40GbE? So I would need to grab a MCX414A-BCAT for compatibility with my QSFP 40Gbit networking?
- Is 56Gb infiniband only? If so I need to just ignore this as a thing, right? My CX3 VPI cards also do 56Gbit IB i think.
- If I get a MCX414A-BCAT would it not be capable of 50Gbit (2 lanes of SFP28??)? So would choosing the 414A BCAT over the GCAT be like choosing to give up the second SFP28 on a QSFP28 port, in order to gain QSFP 40Gbit compatibility? No?
- What about 100Gbit? A MCX415A-CCAT is pretty affordable... Is this basically a MCX413A-GCAT but just filling out the second half of the QSFP28? So, maybe same raw bandwidth as a dual port MCX414A but only one port
- I was gonna ask about MCX413A-GCAT vs MCX4131A-GCAT but apparently these are just the same thing.
- Any benefits for moving up to CX5? I see a MCX515A-GCAT (50Gb) is similar price to MCX415A-CCAT (100Gb)
- What about the MCX455A variants? They seem to involve Infiniband so probably what I assumed earlier about IB w.r.t. 56Gbit was wrong.
The thought process motivating this is that I've come to learn that macOS is finally shipping with an mlx5 driver so I need CX4 or better to get out of the box support on macOS, so the idea is to get hardware that will let that point to point operation just work, but I'm also wondering what it would give me in the way of options in the future when SFP28/QSFP28 based infrastructure like switches become affordable. If an option exists where I can have the best of both worlds it would be worth paying a bit more for that I think.
USUALLY it makes the most sense to get the cheapest compatible thing. In this case that would be a $70 MCX413 that is not capable of 50Gb, which saves a few bucks. However, once I move to SFP28 infrastructure such a card will be at a disadvantage compared to their 50 and 100Gb brethren. So it's also reasonable to perhaps spring for a MCX415A-CCAT to get 100Gbit capability which will allow it not to become obsolete quite so early.
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