Very poor transfer speed from server to workstations over LAN (yet the workstations transfer to the server quickly!)

Posted on 2007-07-25
Medium Priority
Last Modified: 2013-11-09
I'm really hoping there is a simple solution to this because I sure can't think of anything.

Picture this:
-I have a couple of physical servers: DPE2650 and DPE2950.  The 2950 is the one with the issues - it's almost brand new and has been acting as our Exchange 2007 server and nothing more since we rolled it out.
-We have a couple of physical switches (3COM 4200 series)
-We have ~50ish workstations spread between the two switches, all on 100mbps ethernet

-DPE2650 is plugged into a gigabit port on one switch.
-DPE2950 (the problem server) is plugged into a gigabit port on the other switch.
-There is a gigabit up/downlink between the two switches.

Transferring files FROM or TO DPE2950 and DPE2650 is a beautiful thing... super fast.  Obviously at gigabit speeds.  A 150 megabyte file is done in under 10-15 seconds start to finish.

Transferring files FROM any workstation that I have tested so far TO DPE2950, works great too.  Speeds are obviously normal for a 100mbps connection... a 150MB file might take a minute or two.

However, I can turn right around and take that very same file I *JUST* transfered from the workstation to the server, and try to transfer it back, and the connection speed is about the most ridiculous thing ever.  1-1.5 hours.  I mean it literally acts about like a 10mbps connection would, if not worse.

I have tested workstations that are located on both of the two switches - the one where the 2650 is (which , again, transfers to and from the 2950 just fine).  All of them so far exhibit the same characteristic.  Well, actually, I take that back.  I haven't seen necessarily that transfering TO the server is reasonably quick on any workstation located on the opposite switch from the 2950, but I have tested 'from' the server as being horribly slow no matter which switch the workstation is on.

So I really am lost here... what in the WORLD could be slowing down information being pushed out of the 2950 to the workstations, but not slow down information coming into the server from any workstation, and not slow down information being pushed in or out to the 2650?

My first instinct is to suspect that there might be something to do with the gigabit connection speed.  Maybe the 2950 is getting tripped up when trying to push info out to a PC that can only accept it at 1/10th of the speed that it would like to push out at?

I dunno... just a guess.

Come to think of it, most PCs here have gigabit capable ethernet cards.  I'm going to try connecting one to a gigabit port on one of the switches and see if uploading from that workstation to the server suddenly becomes lighting quick...

In the mean time, suggestions would be greatly appreciated!

Question by:Threxx
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Author Comment

ID: 19571447
OK update: I moved my workstation to the last free remaining gigabit port on the switch (same switch that the 2950 is connected to) and now connections are fast in both directions.

I did find it odd that it took about 25 seconds, even still, to transfer a 150MB file... I do remember that a 1gbps connection isn't ACTUALLY going to run at 1 gigabit per second, but even if it only ran at 1/4th of that speed (31.25megabytes per second) then shouldn't a 150MB file transfer in no more than 5 seconds?

Can somebody tell me some realistic speeds to expect to achieve over a 1gbps to 1gbps connection and how to test if I'm achieving those speeds?

Well, anyway, regardless - it appears that between the 1gbps on the 2950 and all 100mbps workstations I'm stuck with a 1-1.5 hour long transfer coming FROM the server, and a couple of minutes going back TO the server.  And it also appears that workstations that are experiencing this, once transfered to the gigabit port on the switch, become 'cured', or at least no longer crippled.  Problem is I don't have anymore gigabit ports open on my switch. : (
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Expert Comment

by:Erik Bjers
ID: 19571558
Could be many things:

Disk IO speeds, can play a part in slowing down file transfers
A bad switch port (or bad switch)
Bad cabel
AntiVirus Scanner
A chatty host on the network fluding it with traffic (though you should see slow transfers in both directions with this)


Author Comment

ID: 19571607
Thanks for the reply ebjers
Isn't Disk I/O speed ruled out by the fact that transfers are fast from gigabit to gigabit connection on the LAN?
A bad switch port?  Well I've tried moving the connection for the 2950 to another gigabit port on the switch.  No change that I could tell.  A bad switch altogether?  Hmmm... well, how would I check for that?  I guess maybe I could move the 2950 to the other switch and see what happens.  OK I will try that.
Bad cable?  Well, I did use a different cable at the switch - didn't think about using a different one going from the server to the wall.  If it's a cabling issue IN the wall I could try another line in the wall.
Antivirus scanner?  I've disabled it for the time being to simplify testing with this and some other stuff (backup software, exchange, 07 etc)
I suppose it could be a bad NIC on the server itself?  It has dual NICs and only one is in use.  I might try swapping the cable on the back from the currently used NIC to the other one.
Maybe a driver issue with the NIC?  Any known issues with the standard integrated NICs on the 2950s?

OK so four things I'm going to try (might as well try them both at the same time since I'm shutting the server down every time I'm doing this so I don't upset exchange in any way):
-I will use the other physical NIC
-I will replace the cable going from the server to the wall.
-I will also use a different connection at the wall so it's running on a different cable through the building.  
-I will also try plugging it into a gigabit port on the other switch

I will try these four things either early tomorrow morning or else tomorrow night and report back.
In the mean time if anyone has any other suggestions for me to try - maybe a network scanner/diagnosis type software tool of some sort?  Or would that just tell me what I already know which is that it's slow given certain directions of data travel?
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Expert Comment

ID: 19572352
I would advise you to try diagnose the server with the Dell diagnostics software that most likely came with the server, or that you can download from Dell's support webpages (http://support.dell.com/support/downloads/format.aspx?c=us&cs=04&l=en&s=bsd&deviceid=7603&libid=13&releaseid=R158443&vercnt=4&formatcnt=0&SystemID=PWE_2950&servicetag=&os=WNET&osl=en&catid=-1&impid=-1).

Disk IO is not ruled out because it's a gigabit connection, and could very likely be the problem.

Author Comment

ID: 19572679
Thanks fgande, I will try that as well.  I'm not saying Disk IO is ruled out because it's a gigabit connection, I'm saying it seems like if it hindered the sending of a file from the 2950 to any workstations, then it would likewise hinder the sending of a file from the 2950 to the 2650 or to my now gigabit connected workstation... but it's far faster with those.

Or did I misunderstand you?

Expert Comment

ID: 19572769
You could be right, but are you doing all the testing with the same files? If you are not, then it could be a problem with the disk/area where the files for the slow transfers are. That last sentence I wrote in my previous post was a bit clumsy, but I would not rule out disk IO just yet.

If you are using managed switches, with firewalls and all that, I would make a network map and try to figure out which routes the fast transfers are taking, and which the slow ones are using. I've seen examples of setups where the traffic from a server to another vlan segment has to go thru a firewall running at way slower speeds than the rest of the network, and thus becoming a bottleneck. If you are able to pinpoint the exact routes for the traffic, and then monitor the traffic on all those points, you can find out if the network itself is a problem.
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Expert Comment

by:Erik Bjers
ID: 19577327
Just another thougt on disk IO, defrag the disks on the affectd systems, as a fragment disk can cause slow file transfers.

Author Comment

ID: 19577782
It's a 6-disk RAID 10 array... only a few months old... it should be really really fast... I suppose the Dell diagnostic software will help test disk performance as well?  At one point I tried to run sysoft sandra just for kicks to see what kind of performance it had, but it kept erroring out badly - I just attributed it to being server 2003 R2 x64 and some funky hardware... not what sandra was probably built with in mind...

Anyhow... I'm doubting I'm going to be able to try those things tonight.  I was up working on a DNS issue until 5AM last night so I'm pretty much a walking zombie at this point.  I will resume troubleshooting based on current recommendations hopefully Friday evening.

Thanks again everyone...

Author Comment

ID: 19654794
Update: I have tried almost everything mentioned here with no luck.

I have read on 3com's website about a known issue with their 4200 series switches (which is what we have) handling gigabit inputs and outputting to PCs connected at 100mbps.  Granted that still doesn't make sense why our other gigabit connected servers don't have the same issue as this one.

The switches are about 4 years old and I found a software update for them that was released over a year ago, but the notes say that it STILL doesn't fix this particular issue.  So WTH 3com?  You release a software update for your switches over a year ago with a known issue and still haven't updated it with a fix?

I acquired a brand new Dell 6000 series switch that I'm going to try swapping in to see how that might affect things... I will try to keep this updated as things progress...

Author Comment

ID: 19719478
The Dell 6000 series switches fixed the issue, but I still feel defeated - no real cause was found.  Every possible reason for there being an issue was defeated by some other logic unless you can assume that our 3com switches were somehow only upset by the exact type of signal they were receiving from the gigabit connected broadcom NICs in our poweredge 2950, and not upset by the 2650s.

The new Dell switches seem to handle everything just fine, though granted almost everything is connected at gigabit speeds now - the couple of workstations left without gigabit NICs running at 100mbps are still connecting much more quickly.
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