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networking - Will multiple switches slow transfer speed


I want to create link between a data server (It's more like NAS) and around 300 computers.


Data transferred per day is around 2GB/computer and speed really matters.


If I use a single switch it would 300 Ethernet cables and may be too messy to maintain.


If I use a switch on every 50 computers would it slow down the connection speed?



Answer



If with 'transfer speed' you mean throughput: It should not matter much.


Every extra device will introduce some minor latency (after all some processing is needed, if if it is only very minor). However latency is not the same as throughput.


Compare it with a conversation via a satellite phone. There will be a 3 second lag before someone else can comment on what you said, but if one person just keep talking, telling long (2GB) stories then the slow down will be minimal.


Which means that I would test these setups:



     +-48 port switch ------ 40 computers
B    |
a    +-48 port switch ------ 40 computers
c    |
k    +-48 port switch ------ 40 computers
p    |
l    +-48 port switch ------ 40 computers
a    |
n    ...
e    |
     +-48 port switch ------ 40 computers

Many switches have a connection which allows you to turn several separate units units into one giant switch. That makes management much easier. Much sure that the switches you buy have this feature.


Why 48 ports switches?
It limit the number of devices. (less space, less devices which can break down).


Why 40 computers per 48 port switch?
Future expandability (Computers moving to different rooms increasing local density, added devices such as printers, a free port for debugging etc. etc.


Why not a single 300 port switch?
Good luck finding those...


[Edit] Apparently there are some. I looked up the model mentioned by David, it is about 25K US$... Use these kinds of switches if you absolutely need maximum performance.


If you already have switches without an backplane link you could always to something like this, but that would mean traffic would flow excessively to whatever switch hosts your file-server. That might overload that switch and with will introduce much more latency than needed.




                 1 fileserver
40 computers     39 computers     ...  40 computers
   | | |               | | |              | | |
48 port switch   48 port switch   ...  48 port switch
    |        |     |         |             |       | 
    |        +-----+         +--        ---+       |   Disabled by 
    |                                              |   default
    +----------------------------------------------+


(The long roundabout cable is in case a switch dies. That would cut off all computers on it and to the side from the switch with the fileserver. In which case switches with spanning tree protocol can detect this and automatically enable the workaround link.)


Lastly, there is always the classical tiered setup:



        Fileserver and other servers
                     |
                 CORE SWITCH
                /   |        \
               /    |         \
 48 port switch   switch  ...  48 port switch
      | | |       | | |                | | |
  40 computers    computers   ...  40 computers

This one has the advantage that you have one (very good) switch in the server room, and at least one link from that switch to each floor or each section.


Then you set up a local room with all the switches for that floor. (If needed with multiple switched, tied via a backlink).


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