[Slightly OT?] Performance of SMB over WANs

Urban Widmark urban at teststation.com
Sat Mar 2 03:23:03 GMT 2002

On Sat, 2 Mar 2002, Jason Haar wrote:

> So are you saying that SMB is pretty poor over a WAN and that (basically)
> there's nothing to worry about? My concern is that our choice of using IPSec
> instead of Frame-Relay has caused this "problem". From what you're saying,
> SMB will perform worse over any WAN link as the latency increases...?

Yes, I believe the non-multiplexed request pattern becomes latency
sensitive. If you have overlapping requests and responses you get
something that is much more like the http case.
(At least it is on the back of the envelope I scribbled on ... why anyone
 should listen to me on this is another matter :)

But this is not necessarily the full explanation or the biggest problem
for your setup. It could also be just a config error somewhere.

A network trace on the client side would show where the time is spent and
how the clients are requesting data.

A trace on the server side would show if the server is taking too long 
processing things. Or if it has a big initial cost.

A simultaneous trace would show if something in the middle is eating your
packets, causing TCP timeouts and retransmissions. (Why would it only eat
the SMB packets? Because they are extra crunchy!)

I have seen a misconfigured network where I believe the server would
sometimes try to do some lookup, fail and timeout before processing the
request. Adding a 30s timeout to the start of each file copy doesn't help
(or browse request or ...)


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