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We have a bandwidth limit between a Linux server and a NAS, created using 'tc' with an IP filter.

When writing to an NFS mount of the NAS, rsync claims a very high transfer speed for each file and then waits a long time before acknowledging that everything has finished.

The total time taken is consistent with the QoS limit and the time taken by the same transfer over FTP.

Why does the write to the NFS mount report higher transfer speeds than are actually happening over the network?

How can I monitor the actual bandwidth of the transfer?

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The most accurate way to monitor bandwidth is by looking at the switch ports. If you want to monitor throughput over a long period of time, then you could set up something like mrtg or cacti. Ntop would also be a very good tool to use.

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ack, @Ian Mackinnon if you are looking for a way to only show the nfs bandwith, not the whole network througput, you have to use a protocol analyzer. i think you could use nstats for that – Thomas Berger Jun 28 '11 at 22:24

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