4 ms·

SFP requires less energy than RJ45, only 0.7W/port. The MikroTik 4-port CRS305-1G-4S+IN draws 10-18W.

bcrl 5y ago
That's not entirely true. SFP power consumption depends on the type of SFP. A 10Gbps DWDM SFP+ might draw 1.8W of power. The why for this is actually quite interesting: the lasers used in DWDM SFPs have much more stringent requirements for temperature stability to ensure the light emitted doesn't drift out of spec. In order to achieve that temperature stability, they use a built in peltier to pump heat away from the laser and control the temperature. They're quite the marvel of modern engineering!
- oasisbob 5y ago
  It would have been fun to be a fly on the wall at Cisco when they first realized people were jamming devices with heaters in SPF sockets.
  - eqvinox 5y ago
    Cisco didn't "realize" this was happening, they specified, had manufactured, and sold the very SFPs the GP post is describing. SFP slots in routers are designed with this thermal load in mind. Which is also why plugging a large amount of DWDM optics into a datacenter switch is a bad idea. Datacenter switches are _not_ designed with this in mind. You run into risks of both overheating the switch as well as overloading the PSUs. A small number of high-power optics ain't gonna break the switch though. And: 10Gbase-T SFPs have horrendous power consumption, even worse than DWDM SFPs. At these speeds, the signal over copper is mostly mush, and the PHY contains a none-too-trivial analog & digital signal processor. Which, again, is where limitations for 10Gbase-T SFP usage come from. If at all possible, avoid this shit — there's absolutely no reason to have 10Gbase-T inside a rack, for example. Just use DAC cables or SR optics.
    - oasisbob 5y ago
      I'm being a bit glib, but from the point of view of someone who used SFP optics once in a while, it seemed like the whole "standard" was a bit of a mess. If it was known that vendors would try to push their thermals past what the device cage would support, why not address that better? The general impression I was given is that thermal loads were one of the primary reasons given for vendor-locking pluggable optics, and that the original SFP spec didn't even address it.
- tomnipotent 5y ago
  Except no one is using DWDM for homelabs, as it's usually used for longer distances. The peltier cooler is definitely cool, though.
  - bcrl 5y ago
    True. On general principle I would recommend folks invest in single mode rather than multimode fiber for permanent installs, as the price delta on SFPs is low enough these days. Multimode is a complete pain as it needs to be upgraded for higher speeds every decade. If it's just a couple of patch cables in a home lab, it doesn't matter, but if it's run through a wall...
- gonesilent 5y ago
  It's also a real laser versus a many sfp+ gbics being LED light source now
logifail 5y ago
> MikroTik 4-port CRS305-1G-4S+IN I have two of these at home, they're neat little bits of kit. They're fanless and therefore silent, which is fine until you realise you want to do 10GbE over existing copper cables with something like Mikrotik's S+RJ10 adapter. Then the temps start to rise... So, I've decided to go completely to fibre, even if it means opening up the walls of the house. Just bought a job lot of used ConnectX-3 cards off ebay.
- lostlogin 5y ago
  > ConnectX-3 cards off ebay. Those cards are so good. I got a few after seeing them rated in r/homelab and haven’t looked back. The Synology took one and it was about 1/10th the price the official Synology one was.
  - tomnipotent 5y ago
    > Those cards are so good Agreed. You can find them on eBay for ~$40 a pop, and they work flawlessly on Linux and Windows. I've made a few purchases from the seller "bitsquad" (ships from Kentucky), and he always seems to have Mellanox/Chelsio in stock.
- walterbell 5y ago
  How do you obtain custom lengths of fibre cables that work with ConnectX-3?
  - tomnipotent 5y ago
    Use fs.com, their generic cables work with MikroTik no issue and they do custom orders.
  - eqvinox 5y ago
    The ConnectX-3 cards are not vendor locked in any way. (And even if they were, that'd only affect the SFP, not the cable.)
- secure 5y ago

bcrl 5y ago

That's not entirely true. SFP power consumption depends on the type of SFP. A 10Gbps DWDM SFP+ might draw 1.8W of power. The why for this is actually quite interesting: the lasers used in DWDM SFPs have much more stringent requirements for temperature stability to ensure the light emitted doesn't drift out of spec. In order to achieve that temperature stability, they use a built in peltier to pump heat away from the laser and control the temperature. They're quite the marvel of modern engineering!

oasisbob 5y ago
It would have been fun to be a fly on the wall at Cisco when they first realized people were jamming devices with heaters in SPF sockets.
- eqvinox 5y ago
  Cisco didn't "realize" this was happening, they specified, had manufactured, and sold the very SFPs the GP post is describing. SFP slots in routers are designed with this thermal load in mind. Which is also why plugging a large amount of DWDM optics into a datacenter switch is a bad idea. Datacenter switches are _not_ designed with this in mind. You run into risks of both overheating the switch as well as overloading the PSUs. A small number of high-power optics ain't gonna break the switch though. And: 10Gbase-T SFPs have horrendous power consumption, even worse than DWDM SFPs. At these speeds, the signal over copper is mostly mush, and the PHY contains a none-too-trivial analog & digital signal processor. Which, again, is where limitations for 10Gbase-T SFP usage come from. If at all possible, avoid this shit — there's absolutely no reason to have 10Gbase-T inside a rack, for example. Just use DAC cables or SR optics.
  - oasisbob 5y ago
    I'm being a bit glib, but from the point of view of someone who used SFP optics once in a while, it seemed like the whole "standard" was a bit of a mess. If it was known that vendors would try to push their thermals past what the device cage would support, why not address that better? The general impression I was given is that thermal loads were one of the primary reasons given for vendor-locking pluggable optics, and that the original SFP spec didn't even address it.
tomnipotent 5y ago
Except no one is using DWDM for homelabs, as it's usually used for longer distances. The peltier cooler is definitely cool, though.
- bcrl 5y ago
  True. On general principle I would recommend folks invest in single mode rather than multimode fiber for permanent installs, as the price delta on SFPs is low enough these days. Multimode is a complete pain as it needs to be upgraded for higher speeds every decade. If it's just a couple of patch cables in a home lab, it doesn't matter, but if it's run through a wall...
gonesilent 5y ago
It's also a real laser versus a many sfp+ gbics being LED light source now

logifail 5y ago

> MikroTik 4-port CRS305-1G-4S+IN I have two of these at home, they're neat little bits of kit. They're fanless and therefore silent, which is fine until you realise you want to do 10GbE over existing copper cables with something like Mikrotik's S+RJ10 adapter. Then the temps start to rise... So, I've decided to go completely to fibre, even if it means opening up the walls of the house. Just bought a job lot of used ConnectX-3 cards off ebay.

lostlogin 5y ago
> ConnectX-3 cards off ebay. Those cards are so good. I got a few after seeing them rated in r/homelab and haven’t looked back. The Synology took one and it was about 1/10th the price the official Synology one was.
- tomnipotent 5y ago
  > Those cards are so good Agreed. You can find them on eBay for ~$40 a pop, and they work flawlessly on Linux and Windows. I've made a few purchases from the seller "bitsquad" (ships from Kentucky), and he always seems to have Mellanox/Chelsio in stock.
walterbell 5y ago
How do you obtain custom lengths of fibre cables that work with ConnectX-3?
- tomnipotent 5y ago
  Use fs.com, their generic cables work with MikroTik no issue and they do custom orders.
- eqvinox 5y ago
  The ConnectX-3 cards are not vendor locked in any way. (And even if they were, that'd only affect the SFP, not the cable.)
secure 5y ago