[c-nsp] Centos upload speed slower on 1000m than 100m over WAN links

Paul paul at gtcomm.net
Mon Jun 28 23:53:10 EDT 2010


Yeah I've checked everything possible that i can think of.
No matter how i test locally, it's fast.  As long as the latency is less 
than 10ms so far it's fast everywhere I've tested.
I wish I could generate 25ms+ latency over a local link somehow and test 
that.

Lee wrote:
> On 6/28/10, Joe Loiacono <jloiacon at csc.com> wrote:
>   
>> OK I'm jumping in on this thread late as I just got back from some
>> vacation, don't know if this particluar observation has been discussed,
>> but ...
>>
>> We've seen this problem a lot when moving up to new local connection
>> speeds. The problem for us has been that unless the entire path can
>> support the new speed (e.g., 1G) switches down the path that connect to
>> slower speeds (e.g. 100M) will overflow and put your data transfer into
>> TCP slow-start recovery. As soon as the sending NIC is 'downgraded' (e.g.,
>> back to 100 M) the overflows disappear, slow-start is avoided, and
>> performance improves. Bitterly ironic.
>>     
>
> Have you checked to see if selective acks are enabled on both sides of
> the connection[s]?
>
> Lee
>
>
>   
>> Joe
>>
>>
>>
>> From:
>> Paul <paul at gtcomm.net>
>> To:
>> cisco-nsp at puck.nether.net
>> Date:
>> 06/27/2010 03:08 AM
>> Subject:
>> [c-nsp] Centos upload speed slower on 1000m than 100m over WAN links
>>
>>
>>
>> I'm not even sure this is the right forum but since we use mainly Cisco
>> equipment I'll give this a shot. :)
>> I have tried several centos based servers and compiled various kernels
>> and the results have been extremely weird.
>> 90% of the cases the remote hosts can download from a server at
>> 1-5megabytes per second, and most of these are over
>> the internet ranging from 30-200ms away.  Local (1ms or less) is super
>> fast 100MB/s for example.
>> Ok that sounds normal since it's going over the internet, etc.  But
>> here's the )(!@*! part..
>> If I set the port speed to 100 megabits full duplex on the switch and
>> server , the clients that get 1-5MB/s now get 11MB/s which is
>> approximately the limit of the 100mbit port.
>> Totally stumped here, tried different nics, servers, even 4 different
>> switches.  Is a very interesting problem and I'm probing to see
>> if anyone else has encountered it.
>> So far the only OS i have tried is centos, but different versions and
>> kernels and hardware.
>> All the switches/routers are Cisco based, but I seriously doubt that has
>> anything to do with this. :P
>>
>> --
>> GloboTech Communications
>> Phone: 1-514-907-0050 x 215
>> Toll Free: 1-(888)-GTCOMM1
>> Fax: 1-(514)-907-0750
>> paul at gtcomm.net
>> http://www.gtcomm.net
>>
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>>     
>
>   

-- 
GloboTech Communications
Phone: 1-514-907-0050 x 215
Toll Free: 1-(888)-GTCOMM1
Fax: 1-(514)-907-0750
paul at gtcomm.net
http://www.gtcomm.net 



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