10GBase-T: Best to avoid it if you can

[Etorix]

@da_da Playing with filters on FS products page, I eventually found out
$189 QSFP28 100GBASE-CWDM4 module for SMF, duplex LC
to be compared with
$99 QSFP28 100/112GBASE-SR4 module for MMF, MTP/MPO-12
$399 QSFP28 100GBASE-SR BiDi SWDM4 module for MMF, duplex LC
$439 QSFP28 40/100GBASE-SM4 SWDM4 module for MMF, duplex LC

Is this what you mean? An option for single mode fibre which allows to upgrade to higher speed while keeping existing cables with the usual LC connector, without requiring all new MTP cables, as in the budget-friendly multimode option, and without breaking the bank to the same extent as the solutions for multimode LC cables.
Assuming there are no further driver issues with all these different protocols, and depending on the number of posts, it could be half-convincing.

(Admittedly, the issue goes beyond 10GBase-T vs. SFP+, but is at least relevant to the planning of an optical network for initial use with SFP+ —and possibly more later. And I'd like to understand the possible case for single mode over multimode in a home network.)

 

[Ericloewe]

Oh wow, the 100GbE transceivers that use duplex LC are actually cheaper than the 40GbE ones.

 

[jgreco]

Oh wow, the 100GbE transceivers that use duplex LC are actually cheaper than the 40GbE ones.

And will be cheaper on the used market in a few years, in many cases. Long haul circuits (really anything beyond SR distances, up to 10km) in data centers are relatively common because the limit on SR is about 250-400m (technically 300m but this gets bent a good bit). The really expensive optics tend to be ER (10-40km) and ZR (40-80km). But the thing to understand here is that it is the limit on SR distance that makes LR attractive in some cases. It is NOT that weird to have needs, especially in large scale facilities such as DuPont Fabros/Digital Realty, where you run out of cage space and have to add another, possibly even in another building. Certain areas of the country like Ashburn VA have large tracts of space dedicated to data centers:

and you can see all the various data center properties; I selected this zoom level for readability but you can see many more, some may be several kilometers away, by searching for the super secret "21715 filigree court" and then scrolling around -- not kidding, at one time, decades ago, they did not want the location publicized. The point is that even within many of these facilities, it is easy to exceed 300m and for interconnects between them, you need LR. So some folks, because the tech industry is not always cost sensitive, will just do EVERYTHING with LR and then not worry about it. In a few years when the next hotness comes along, then you may be finding those relatively unwanted optics up on the used market at a good price.

 

[Ericloewe]

And will be cheaper on the used market in a few years, in many cases.

They already are. 1st gen Finisar 100GBase-LR modules are being dumped on eBay for under 10 bucks a pop. I guess a few big customers mass migrated to 200/400GbE recently.
In a way, 40GbE feels a lot like 10GBase-T, minus the being a complete dead-end part: never popular enough to get really cheap, obsoleted by newer stuff.

because the limit on SR is about 250-400m (technically 300m but this gets bent a good bit)

Yeah, it doesn't take much to blow past the limits of multi-mode fiber. We need to connect a couple of buildings and structures within the same complex, and visually they're "right over there", but once you consider conduit runs inside the buildings and then the actual run between buildings, that stuff adds up quickly. To make matters worse, old OM2 is essentially useless for even 10GbE over any meaningful distance (I'm told the cost of transceivers back in the late 2000s/early 2010s led to OM2 being chosen instead of OS2, and this was for Gigabit only), so the local team has been rolling out new fiber cables to be able to run a measly 10GbE connection between buildings.