Weird LAN behavior v.slow transfer speed

Discussion in 'OT Technology' started by deusexaethera, May 21, 2008.

  1. deusexaethera

    deusexaethera OT Supporter

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    So I have some servers in my server rack. For some reason that I have yet to figure out, SMB (windows fileshare) transfers from ServerA <=> ServerB and ServerA <=> ServerC are going ridiculously slow, yet I know the servers' physical connections are good because SMB transfers between any of those servers and any other machines on the LAN are blazing fast. So there's something somewhere that's interfering with transfers specifically between those three servers, and it's not Group Policy or LMHOSTS.

    What else could it be?
     
  2. JayC71

    JayC71 Guest

    Is SMB signing enabled between the servers? That will slow down SMB transfers.
     
  3. deusexaethera

    deusexaethera OT Supporter

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    SMB signing? I've never even heard of that.

    It's not like it's running kinda slow, it's acting like it's having trouble even finding the other server it's trying to transfer to/from. It also drops the connection on a regular basis, making large file transfers effectively impossible.
     
  4. JayC71

    JayC71 Guest

    http://support.microsoft.com/kb/887429

    It requires extra processing of SMB packets, hence slower. If you're having problems connecting period, it's probably not your problem. How are the server connected to each other? It's probably some form of a networking or routing issue.
     
  5. 5Gen_Prelude

    5Gen_Prelude There might not be an "I" in the word "Team", but

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    I had old VLAN settings in a switch do that to me...
     
  6. deusexaethera

    deusexaethera OT Supporter

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    Hmm. The switches I have (claim that they) don't support 802.11q, so VLAN shouldn't be an issue. I suppose I can always reboot the switches, though.
     
  7. P07r0457

    P07r0457 New Member

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    802.11Q is a wireless standard. So not sure what the fuck that has to do with anything!

    802.1Q is VLAN trunking which would allow hosts across multiple VLANs share one physical network connection (establishing a trunk) by "tagging" each packet to specify the destination VLAN.

    Note that you *CAN* still use VLANs even without 802.1Q. You simply would not have the tagging/trunking functionality.
     
  8. critter783

    critter783 OT Supporter

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    Out of curiosity, what kind of servers are they? We had a similar problem here for a while.
     
  9. deusexaethera

    deusexaethera OT Supporter

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    I meant 802.1q, dammit. Anyway, I'm going to have to read up on VLANs; from what you've said, I've got about three different ideas of what it does.

    ...

    Oh shit. You know what, all three servers are VM servers. I bet that means they use 802.1q to figure out which physical NIC card to send packets to for the VMs to receive.

    ...

    :doh: ...and the three machines are all plugged into the same switch. There's a fourth VM server, but it's on a different subnet and therefore a different switch, and it doesn't have any problems at all. I'm increasingly suspicious of this VLAN tagging thing.
     
  10. deusexaethera

    deusexaethera OT Supporter

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    2x Dell PowerEdge 2950, running WS2003x64, and 1x Dell PowerEdge 2900, running Windows Storage Server. All three have Broadcom Gb/s NIC cards.
     
  11. deusexaethera

    deusexaethera OT Supporter

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  12. P07r0457

    P07r0457 New Member

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    you're using broadcom network cards? Shit I coulda told you that was a problem.

    Intel NICs are the way to go.
     
  13. critter783

    critter783 OT Supporter

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    The problem we had was that the servers were frequently trying to re-negotiate speed and duplex. Turning the NICs from auto to fixed 100 Full Duplex solved the problem. I'd say it's worth a shot.
     
  14. deusexaethera

    deusexaethera OT Supporter

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    All of the feedback indicates that has nothing to do with it. It's at least partly the TCP/IP Offload Engine, perhaps other stuff too.

    I'm wondering if I shot myself in the ass by buying a switch that doesn't support 802.1q when I'm trying to run ~4 VMs per host machine.

    EDIT: If it makes you feel any better, all my workstations are using Intel NICs.
     
  15. deusexaethera

    deusexaethera OT Supporter

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    Nah, I can't do that. The whole point of my network upgrade efforts over the past few weeks was to take advantage of the Gb/s wiring we had installed a few months ago.
     
  16. critter783

    critter783 OT Supporter

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    Then set it to 1000/Full. The point was that for our Dell servers, they were re-negotiating so often that the TCP slow-start was never getting up to speed and was even causing connection timeout issues.
     
  17. deusexaethera

    deusexaethera OT Supporter

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    Oh, I see what you're saying. Well, I can take a look at that and see if that's the other part of the problem.

    However, removing the TCP/IP Offload Engine license keys definitely stabilized things. It's now transferring at a stable 2Mb/s and not losing connectivity, which isn't great, but it's okay.
     
  18. deusexaethera

    deusexaethera OT Supporter

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    Well, it looks like I've fixed it. Apparently I did shoot myself in the ass by buying a switch that doesn't support VLANs, because as soon as I took the license-server VM off the file server and put it somewhere else, all of a sudden the file transfers from the file server to the two VM servers shot back up to about 45Mb/s -- right where it should be.

    My setup just doesn't like having multiple VLAN recipients at both ends of the physical connection.
     

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