Slowdown when copying large files

[Stephen L Arnold]

On the Samba list Michael Anthon asked:

> Further to my previous post, I have made an interesting
> discovery.  This particular slowdown only occurs from clients
> that are running Windows 98.

Have you read through Speed.txt and Speed2.txt?  I know it's not 
the clearest of documentation, but I eventually figured out that 
the TCP/IP settings on the windoze client can cause serious 
problems with reading/copying files.  Specifically, the RWIN 
(DefaultRcvWindow) setting must be above ~3072, at least for a 
win95 client.  The Speed docs also mention that a setting *above* 
that value can also cause problems for some clients.  It must be at 
least somewhat hardware-dependent (eg, I have fast (PII) clients 
talking to a slow (466-100) server.  Your mileage may vary.  All I 
know is, the default RWIN setting (MaxMTU=576, MSS=536, RWIN=2144) 
of 4 times MSS was killing my samba browsing (eg, opening files on 
a samba share with windoze explorer).  When I bumped it up to 8xMSS 
(RWIN=4288) everything started working fine with samba (and the 
modem throughput is fine as well).  If you haven't made the windoze 
DUN TCP/IP tweaks on the clients (ie, you've still got the default 
MTU of 1500 and no other parameters set) I don't know what to say.  
You could always try *lowering* RWIN...  (Hey, it's worth a shot :-)

Hope this helps, Steve Arnold



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Stephen L. Arnold                               Systems Engineer
ENSCO Inc.                        email:  arnold.steve at ensco.com
P.O. Box 5488                         www:  http://www.ensco.com
Vandenberg AFB, CA  93437             voice: 805.734.8232 x68838
                                               fax: 805.734.4779
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