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How much bandwidth utilization % affects throughput

Posted on 2013-12-10
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Hi All,

We have a 3750x switch stack & Im getting a number of questions around the possibility that our switch ports 1Gb switch ports are causing a bottleneck...

When I look into the statistics we average around 250Mbps (so around 25%)  Occasionally we peak around 80-90% during nightly backup windows...

So even the question is...

Can higher utilisation cause latency/bottleneck even though its not at 100% ?

Im not sure how much to allow for TCP overheads etc but Im pretty sure that unless its not hitting 100% in both duplex directions then there shouldn't be a problem ??

Thanks
T4K
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Question by:Thirst4Knowledge
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by:giltjr
ID: 39709385
How long are you running at 80-90%?

Is your measurement period the normal 5 minute interval?

Remember these are based over bits over time and you are really either at 100% or 0%.  The utilization is based on how long you are at 100 vs. 0.

When running at 80-90% that means that for 80-90% of the measurement period you were at 100% utilization and 10-20% of the measurement period you were at 0%.
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by:Thirst4Knowledge
ID: 39710258
Ok now im really confused.

Correct me if Im wrong, so what your saying is that if any utilisation is showing then it means you are running at 100% ?

For example when it  shows 1% utilisation then its actualy 100% utilisation ??

or are you saying this is only the case for anything about 80% utilisatioin?
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giltjr earned 2000 total points
ID: 39710362
--> For example when it  shows 1% utilisation then its actualy 100% utilization ??

Well, for some period of time during the time period measured yes it was 100% utilized.  However for some period of time during the time period measured it was also 0% utilized.

Remember utilization is the total amount of a available resource minus amount of resource used divided by time.

Look at like a light bulb.  Either the light is on or it is off, there is no in between.  When it is on it is 100% utilized, when it is off it is 0% utilized.   Over a 10 hour period if the light bulb was on for 1 hour and off for 9 hours it was 10% utilized over 10 hours.  However it was 100% utilized for 1 hour and 0% utilized for 9 hours.

When sending data over the network you can't slow down the flow of electrons or photons.  So on a 100 Mbps link if you are sending data it is flowing at 100 Mbps, it can't flow at 90 Mbps or 1 Mbps or any other speed than 100 Mbps.  That is, it is either on or it is off.

So, if the link was 90% utilized for 3 hours that means for a total of162 minutes the link was 100% utilized and for a total 28 minutes it was 0% utilized.
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