samba - May 2005 - excessive TCP retransmissions with samba 3.0, slow file opening

Hello all!

I've got a Fedora Core 3 box running Samba 3.0.8.
It serves a variety of roles, including mail server and samba server.
The mail server is quite fast, but the smb server generates lots and lots of TCP
retransmissions (as seen in ethereal).  The general consensus is that this is
new in the last few weeks.  One user has been reporting speed problems for some
time, but no metrics were ever gathered.

I've tried replacing the NIC, but the problem follows.  This is a small
network, with two 100mbit hubs, and windows 2000 on all the clients.

I want to suspect hardware, but flood pings from a linux box put on the network
never report dropped packets.

All hosts are listed in DNS, and reverse DNS lookup is successful.  I've
also configured samba to pass WINS requests on to DNS.

I'm absolutely stumped.  I don't see the retransmissions with anything
on the network except SMB-related TCP traffic.

I don't see anything peculiar in  /var/log/messages or the smbd.log file. 
nmbd is running just fine.

Any assistance is greatly, greatly appreciated.

Jeremy
-- 
Jeremy Anderson		jeremy (at) angelar.com	
http://www.angelar.com/~jeremy

>I've tried replacing the NIC, but the problem follows.  This is a small
network, with two 100mbit hubs, and windows 2000 on all the clients.
>  
>
Hubs? HUBS? I hope you meant switches. If not, go buy some switches.
>I want to suspect hardware, but flood pings from a linux box put on the
network never report dropped packets.
>  
>
Then go back to hardware.  Unless you've got firewalls or something in
the mix that's probably where your traffic is going.  Watch the
collision lights on your hubs and see if they go nuts when the problem
occurs.
>I'm absolutely stumped.  I don't see the retransmissions with
anything on the network except SMB-related TCP traffic.
>  
>
SMB is pretty chatty as far as protocols go.

-- 
Paul Gienger                    Office: 701-281-1884
Applied Engineering Inc.
Systems Architect               Fax:    701-281-1322
URL: www.ae-solutions.com       mailto: pgienger@ae-solutions.com

>I've tried replacing the NIC, but the problem follows.  This is a small
network, with two 100mbit hubs, and windows 2000 on all the clients.
>  
>
Hubs? HUBS? I hope you meant switches. If not, go buy some switches.
>I want to suspect hardware, but flood pings from a linux box put on the
network never report dropped packets.
>  
>
Then go back to hardware.  Unless you've got firewalls or something in
the mix that's probably where your traffic is going.  Watch the
collision lights on your hubs and see if they go nuts when the problem
occurs.
>I'm absolutely stumped.  I don't see the retransmissions with
anything on the network except SMB-related TCP traffic.
>  
>
SMB is pretty chatty as far as protocols go.

-- 
Paul Gienger                    Office: 701-281-1884
Applied Engineering Inc.
Systems Architect               Fax:    701-281-1322
URL: www.ae-solutions.com       mailto: pgienger@ae-solutions.com

<quote who="Jeremy Anderson">
> Hello all!
>
> I've got a Fedora Core 3 box running Samba 3.0.8.
> It serves a variety of roles, including mail server and samba server.
> The mail server is quite fast, but the smb server generates lots and lots
> of TCP retransmissions (as seen in ethereal).  The general consensus is
> that this is new in the last few weeks.  One user has been reporting speed
> problems for some time, but no metrics were ever gathered.
Jeremy,

I have a similar problem at one of my clients.  The problem is mainly with
a piece of software called Proseries (by Intuit).  The software takes 3-5
minutes to open on two of the machines on the network.  one of them is
brand new.  The third machine has no problem at all.  It's not the oldest
either.  Go figure.  I'll replace the hub and see if that helps.

If you get a solution, please let me know.

Jeremy Anderson wrote:
> Hello all!
> 
> I've got a Fedora Core 3 box running Samba 3.0.8.
> It serves a variety of roles, including mail server and samba server.
> The mail server is quite fast, but the smb server generates lots
 > and lots of TCP retransmissions (as seen in ethereal).  The general
 > consensus is that this is new in the last few weeks.  One user has
 > been reporting speed problems for some time, but no metrics were ever 
gathered.
> 
> I've tried replacing the NIC, but the problem follows.  This is a
 > small network, with two 100mbit hubs, and windows 2000 on all the 
clients.
> 
> I want to suspect hardware, but flood pings from a linux box 
 > put on the network never report dropped packets.
> 
> All hosts are listed in DNS, and reverse DNS lookup is 
 > successful.  I've also configured samba to pass WINS
 > requests on to DNS.
> 
> I'm absolutely stumped.  I don't see the retransmissions
 > with anything on the network except SMB-related TCP
traffic.
> 
> I don't see anything peculiar in  /var/log/messages or the 
> smbd.log file.  nmbd is running just fine.
> 
> Any assistance is greatly, greatly appreciated.
> 
I'd like to thank everyone for the help with this problem.  Replacing 
the two Ethernet hubs with a single Ethernet switch seems to have 
resolved the problem.  The two hubs were actually hot to the touch
when I looked at them.  I wouldn't have guessed that hardware would
affect just a single protocol, but it looks like only SMB was
chatty enough to overload the failing hubs.

-- 
Jeremy Anderson		jeremy (at) angelar.com	
http://www.angelar.com/~jeremy