Large network latency


On a FAS2520 iSCSI attached storage (1Gbps active link, 1Gbps passive). 10G Base-T ports used on 1Gbps speed. Switch Cisco SG500. Host is - VMware esx.

I see high latencies. VMware latency are up to 25ms, I think it is because vmware averages that.

qos statistics shows high latency on network layer. Can anybody explain what can cause high network latency?


qos statistics latency show output, latency can be up to 140ms, but is much lower in avg.


Policy Group            Latency    Network    Cluster       Data       Disk        QoS      NVRAM
User-Best-Effort        46.53ms    45.11ms        0ms   301.00us    87.00us        0ms  1033.00us


It is not because 1Gbps is full see statistics run from two CLI windows simultaneously:


Latency up to 23ms:

qos statistics latency show

Policy Group            Latency    Network    Cluster       Data       Disk        QoS      NVRAM
User-Best-Effort        22.96ms    22.11ms        0ms   210.00us    71.00us        0ms   573.00us

No much output:

qos statistics performance show

Policy Group             IOPS      Throughput    Latency

User-Best-Effort          202        8.77MB/s    23.26ms



I did not find any errors in ifstat -a output. Links run at 1Gbps.

Thank you.


Re: Large network latency



Check the following 2 KB articles which give indepth knowledge on Network Configuration and Lun latency.



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