Dell PowerFlex 4.5.x CLI Reference Guide

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Understanding the effect of network latency on NVMe over TCP latency counters

This section describes the possible effects of network latency between the host and storage data target (SDT) in an NVMe over TCP environment.

To access the performance counters, run the following commands:

For storage data target

scli --query_properties --object_type SDT --all_objects --properties SDT_DATA_READ_LATENCY,SDT_DATA_WRITE_LATENCY,SDT_HOST_READ_LATENCY,SDT_HOST_WRITE_LATENCY

Output sample:

754135e800000000:
          SDT_DATA_READ_LATENCY		     3595 IOPS 0.823 ms average latency 
          SDT_DATA_WRITE_LATENCY	     0 IOPS 0 us average latency 
          SDT_HOST_READ_LATENCY		     899 IOPS 82 microseconds average latency 
          SDT_HOST_WRITE_LATENCY	     899 IOPS 12 microseconds average latency

For host:

scli --query_properties --object_type HOST --all_objects --properties USER_DATA_SDC_READ_LATENCY,USER_DATA_SDC_WRITE_LATENCY

Output sample:

f3e742f300010000:
          USER_DATA_SDC_READ_LATENCY	    930 IOPS 69 microseconds average latency
          USER_DATA_SDC_WRITE_LATENCY	   930 IOPS 12 microseconds average latency

Table 1. I/O latency measurement by countersThe following table shows the I/O latency that each counter measures.
PowerFlex object	Performance counter	Measures I/O latency
PowerFlex object	Performance counter	Type	From	To
storage data target	SDT_DATA_READ_LATENCY	Read	SDS	storage data target
	SDT_DATA_WRITE_LATENCY	Write	storage data target	SDS
	SDT_HOST_READ_LATENCY	Read	storage data target	Host
	SDT_HOST_WRITE_LATENCY	Write	Host	storage data target
HOST	USER_DATA_SDC_READ_LATENCY	Read	SDS	storage data target
HOST	USER_DATA_SDC_WRITE_LATENCY	Write	storage data target	SDS

NOTE:The term storage data client (SDC) used in the counter name is for backward compatibility purposes only.