network speed/duplex settings on virtual machines

[gwelsh123]

Hello

we are using a virtual switch, with 4 x 1 gigabit NICs, physical switch ports are configured as 1 gig/full duplex

All VMs have been setup as default, latest vmware tools installed, VMs reporting network link speed as 1.0Gbps (as to be expected)

A user complained that copying files to a vm (windows 2003) took a long time, and on the properties of the NIC (within the VM), the FULL DUPLEX option was set to 'use adapter settings'. This was set to AUI - FUll Duplex, and there was a marked increase in performance, worrying, since all our VMs (over 100) have been setup out the box, with no extra config being done on the adapter settings

Should adapter settings be configured? i thought this was just a virtualised driver, and what was configured on the NIC had no impact on network performance?

Is anyone modifying these settings?

[esiebert7625]

You should not need to modify the VM NIC settings. Make sure your physical NIC settings match your physical switch. For gigabit you should use Auto/Auto for best results.

Network cards – Used Auto or Fixed Speed and Duplex - http://www.vmware.com/community/thread.jspa?messageID=568366&#568366

[gwelsh123]

after subsequent testing, it seems setting these duplex settings was a red herring

copying filex (around 200Mb) to the VM, first took about 1 minute

filex was deleted, and recopied, it then copies pretty quickly (speed as expected), so it seems chaning this had no effect (as you would think)

it looks like its being cached somewhere? (same test was done on a physical windows box, there was no difference in the time taken to copy the file)

i take it by auto/auto you mean the physical NICs attatched to the virtual switch? we have them set to 1000 Full

[esiebert7625]

There is no caching that is done. Are you sure you are not experiencing period peaks which is impacting performance? Maybe another VM has high network traffic at the time of the slow copy? What load balancing scheme are you using on your vSwitch, IP Hash seems to work the best. If you are copying between VM's on the same vSwitch then the traffic does not go over the network, it stays inside the vSwitch.

Yes the physical NIC's that are attached to the vSwitch should be set to Auto/Auto for Gigabit. Also make sure your physical switch matches this if you change them.

You might also check out this huge thread...

http://www.vmware.com/community/thread.jspa?threadID=77227&start=0&tstart=0

[gwelsh123]

we see the same behaviour in our lab environment (copying filex is slow, subsequent copies of that file run fine), in the lab we are using 100Full (fixed) physical switches.

i will have a look at this thread

we are using ip hash as the load balancing method.

i dont think network is being over utilised at this point, the file copy was from a physical server to a virtual, its been seen on a number of VMs, all running on different esx servers...

i am starting to think that ths may be a disk write issue.

[esiebert7625]

That is indeed possible, disk is usually the first bottleneck, especially if you are using local disk instead of a san. You might look at some of the disk performance stats in VC for the ESX host that the VM is on.

[IB_IT]

I was looking at similar issue with my sql server. Took perfmon metrics and there were no bottlenecks. My app engineer kept complaining of slow response times. I tested a few copies (200 MB file) up to this server and it took about 30 minutes. I then tried to copy the same file to other VM's and found the same issue.

I changed my DESKTOP NIC settings from auto to 100 FULL and BLAM...copied the 200 MB file up in about 15 seconds.

Not completely convinced that the issue is resolved, but just giving a different perspective...may not always be the server...may want to check your clients.

[TomHowarth]

do you have a DNS issue, that could explain the first copy being slow and subsequent ones being faster. once the VM has cached the address of the recieving server it will no longer have to find it

[AmeerFaisal]

How do I achive above 1Gig link speed in Virtual machines as my physical NIC card supports 10 Gig

Thank you