On Sat, Feb 2, 2019 at 10:18 AM <tlaro...@polynum.com> wrote: > > Hello, > > I have a NetBSD serving FFSv2 filesystems to various Windows nodes via > Samba. > > The network efficiency seems to me underpar. > > There is very probably Samba tuning involved. Windows tuning too. But a > question arised to me about miscellaneous speeds of ethernet cards > connecting to a card on the NetBSD server able of auto-selecting the > speed between 10 to 1000. > > The Windows boxes are very hetergoneous (one might even say that there > are not too same Windows OS versions, because some hardware is quite > old) and the cards range from 10 to 1000 able ethernet devices. > > Needless to say, there is a switch (Cisco) on which all the nodes are > connected. > > When concurrent accesses to an auto-select ethernet card are done by > ethernet cards ranging from 10 to 1000 speeds, are is this handled by > the card? > > Is the speed adapted to each connected device? Or does the serving card > fix the speed, during a slice of time, for all connexions to the minimum > speed? > > What is the "cost" of switching the speed or, in other words, is > connecting a 10base card able to slow done the whole throughput of the > card even for other devices---due to the overhead of switching the speed > depending on connected devices? > > (The other question relates to the switch but not to NetBSD: does the > switch have a table for the connected devices and buffers the > transactions, rewriting the packets to adjust for the speed of each of > the devices?). > > If someone has any clue on the subject, I will be very thankful to > learn!
As you probably suspect, this isn't a NetBSD issue, and is something you can read on extensively on the internet. Maybe you need a place to start, which is often where I find myself on many subjects. I probably will miss something. The switch negotiates connections on a port by port basis. So if one device is 1 gig, it will negotiate 1 gig. If another device is 10 megabit, it will negotiate that. Each port is a separate entity. Then you have half vs. full duplex. So what happens when they talk? The switch does something at layer 2 called RED or WRED (Weighted Random Early Detection) to decide if one port is going too fast for another. It's not really an ideal place to be, and it usually happens when either you have different adapter speeds or you have a whole lot of machines on lots of ports trying to overrun 1 port (like an uplink port). But you're hoping it doesn't come to that. It's best if TCP just does it's thing and sets the window size to one that both sides can handle nicely and things "just work". RED or WRED will happen but hopefully less. I'd love someone to correct me if I'm wrong on this. If you're asking if using a 10 megabit adapter is the best way to do traffic shaping, it isn't, and that's a whole different subject that probably doesn't belong here. Andy
