0

i followed this thread to get the information on reading NIC speeds. How do I verify the speed of my NIC?

i am using ethtool to verify the speed of my NIC as discussed the thread.

:~ # ethtool eth0
    Settings for eth0:
    Supported ports: [ TP ]
    Supported link modes:   10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
    Advertised pause frame use: No
    Advertised auto-negotiation: Yes
    Speed: 1000Mb/s
    Duplex: Full
    Port: Twisted Pair
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    MDI-X: off
    Supports Wake-on: d
    Wake-on: d
    Current message level: 0x00000007 (7)
                           drv probe link
    Link detected: yes


:~ # dmesg |grep eth0
[    5.347423] e1000 0000:02:00.0: eth0: (PCI:66MHz:32-bit) 00:50:56:8b:26:0e
[    5.347533] e1000 0000:02:00.0: eth0: Intel(R) PRO/1000 Network Connection
[   43.467863] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
[3656340.307349] e1000: eth0 NIC Link is Down
[3656340.312386] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
[30612796.474526] device eth0 entered promiscuous mode
[30612946.780348] device eth0 left promiscuous mode

i know that, this is a virtual machine and the NIC should be simulating a 1000Mbs speed. That makes 128MB for 1 second and this should be my bottleneck, for every NFS related transfer which is made over this host. (is this correct so far?)

I mounted a Netapp NFS share to this host and started writing a file. It is a network share, so the speed should be limited by the bottleneck created by the NIC.

> time ; dd if=/dev/zero of=/test/1GB_file bs=1GB count=1
1.032u 27.065s 7:08:35.06 0.1%  0+0k 203632+27343968io 43pf+0w
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 3.92766 s, 255 MB/s

i repeated the dd command on and on, and it was always around 250MB/s. A way higher than 128MB/s == 1000Mbps.

What am i missing? Why is this number higher than the network bandwidth?

2

In a VM, the NIC speed is not a real limit. If the host can push 2000Mb/s in to a guest, then so be it.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.