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Perfmon Bytes/sec

Hi Experts,

Right now, I'm using Perfmon in my application server. I added a counter Network Interface\Bytes Total/sec in monitoring. The server have gigabit nic. I just want to know the threshold value for it so that I will know if the network is already saturated or causing bottleneck.

Thank you.
2 Solutions
it is a moving target because the limit is a function of other variables, such as collisions & MTU size.  And as for detecting a bottleneck, you can't assume that your system is generating enough disk/IO to eliminate disk, CPU, or something else as the bottleneck.

then you have reads vs writes.  A single metric won't be all that great.  May I suggest reading this document?  

MediaBancAuthor Commented:
Hi Dlethe,

With regards to the link above, the author specified:

For a 100-Mbps NIC, the interface consumed is 8.7MB/sec (100Mbps = 100000kbps = 12.5MB/sec* 70 percent). In a situation like this, you may want to add a faster network card or segment the network

I would like to know how did he come up with the information or how to measure it. I'm confused yet if for a Gigabit NIC, should I multiply it by 10 since it's gigabit?

Thank you.
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David Johnson, CD, MVPOwnerCommented:
As you have seen from the above only getting 70% of the published NIC speed is normal rule of thumb. Also you have to look outside of the single network adapter and use a lan sniffer that typically taps into your ethernet circuit to determine the total network traffic. A bad network adapter can bring your entire network to a crawl by flooding the network with malformed packets. Even a section of bad cable can slow things down measurably.. To get the benefits of CAT 6 you need CAT 6 throughout the network.
First off, Gigabit Ethernet measures its bandwidth as a decimal (i.e. 1,000,000,000 bits), while The OS typically measures in binary (i.e. 1MB = 1048576 Bytes). Also, Perfmon in measuring in bytes, which are 8 bits each (i.e.  1,000,000,000 bits = 125,000,000 bytes) . It's not clear whether Perfmon is measuring MB/sec in binary or decimal, but the maximum bandwdith is either going to be 119.2 MB/sec or 125 MB/sec, respectively.

I don't think the 30% overhead is entirely accurate, as 70% of 125 MB/sec is only 87.5 MB/sec, yet I found an article where there were able to achieve 111.4 MB/sec over gigabit ethernet, which is at most an 11% overhead. The article gives a lot of info on the upper limit of gigabit ethernet based on real-world tests, and shows that it's more likely that things like disk performance are going to be the bottleneck in utilizing the bandwidth:

Instead of measuring the total Bytes/sec, this page suggests monitoring the "Output Queue Length", since that would suggest whether the network adapter is getting more traffic than it can handle:
To see if this is becoming a networking side bottleneck, check the results of "output queue length" under the network interface object in perfmon for the specific network interface in question. If your output queue lengths are rising and steadily above 0 there could be a saturation issue.

The Technet article dlethe linked to also suggests monitoring this counter:
Network Interface\Output Queue Length This measures the length of the output packet queue, in packets. There is network saturation if the value is more than 2.
one can get > 100Mbytes/sec on ethernet, but that requires nailing MTU, having a switch, no collisions, and manipulating traffic so that  each packet has max payload size.  I can get that easily if I write low-level UDP socket code, but you won't be doing that.

Real-world, figure anything pushing 90MB/sec is the best you can expect unless you are running benchmarks.

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