We have 2 x Dell 5524 switches configured as a stack. Only 8 ports are in use on each switch (5 of the ports are used for the same servers which have two NIC's configured as a team set failover redundancy).
The firmware version of both switches is 4.1.0.5
The 5524 stack uplinks via a 10GB Fibre link to 2 x 5548 switches also configured as a stack.
RSTP and port fast is switched on for all ports on both switches except the uplink..
We have set the Root path cost to 20000 on the 5548 and 40000 on the 5524.
When I run psping latency test using 8k packets between two R520 servers on the 5524 stack we see 99% of the packets return within less than 1 ms but the rest range from 1 up to 280 ms.
We would expect latency between ports on the same switch to always be below 1 ms. (The servers are not heavily loaded).
Can anyone explain this high latency? Is this expected for a few packets in every 10000? I run the same latency test on other networks with similar switches (not stacked) and all packets come back with less than 5 ms.
C:\Support\PSTools>psping -l 8k -n 10000 -h 172.18.3.162:9999
PsPing v2.01 - PsPing - ping, latency, bandwidth measurement utility
Copyright (C) 2012-2014 Mark Russinovich
Sysinternals - www.sysinternals.com
TCP latency test connecting to xxx.xx.x.162:9999: Connected
10005 iterations (warmup 5) sending 8192 bytes TCP latency test: 100%
TCP roundtrip latency statistics (post warmup):
Sent = 10000, Size = 8192, Total Bytes: 81920000,
Minimum = 0.75ms, Maxiumum = 186.03ms, Average = 1.23ms
Latency Count
0.75 9940
10.50 19
20.26 19
30.01 6
39.76 4
49.51 3
59.26 2
69.01 1
78.76 1
88.51 0
98.26 2
108.02 1
117.77 1
127.52 0
137.27 0
147.02 0
156.77 0
166.52 0
176.27 0
186.03 1