5020 - Latency Tests

The Nexus 5000 is a very low latency (cut through) 10 gbps switch.  From all of the performance tests I've seen, it lives up to the marketing numbers.  But, all of these tests have focused on the 10 gbps performance.  The 5000 also includes some 1 gbps ports for legacy connectivity, but based on the latency numbers posted below, they operate in a store and forward manner.  Here is a quick reference for the switching modes between various interfaces:

From	To	Mode
10G	10G	Cut-Through
10G	1G	Cut-Through
1G	10G	Store and Forward
1G	1G	Store and Forward

The test used was very simple.  The default config is in place, ports 1 and 2 have been placed in a common VLAN, the port speed was adjusted for 1 gbps connectivity, and the appropriate STP port type has been configured.  Below are the results.

Please note:
    1. Latency values are listed in microseconds
    2. Frame sizes do not count the Inter Frame Gap and MAC Preamble

Frame Size	Load %	Min Latency	Max Latency
64	10	3.4	4.0
	20	3.4	3.7
	30	3.4	4.0
	40	3.4	4.1
	50	3.4	3.8
	60	3.4	3.9
	70	3.4	4.1
	80	3.4	4.1
	90	3.4	4.2
250	10	4.9	5.6
	20	4.9	5.1
	30	4.9	5.1
	40	4.9	5.2
	50	4.9	5.1
	60	4.9	5.2
	70	4.9	5.5
	80	4.9	5.2
	90	4.9	5.4
500	10	6.9	7.1
	20	6.9	7.2
	30	6.9	7.1
	40	6.9	7.1
	50	6.9	7.1
	60	6.9	7.2
	70	6.9	7.2
	80	6.9	7.2
	90	6.9	7.3
1000	10	10.9	11.1
	20	10.9	11.1
	30	10.9	11.1
	40	10.9	11.1
	50	10.9	11.1
	60	10.9	11.1
	70	10.9	11.1
	80	10.9	11.2
	90	10.9	11.1
1518	10	15.1	15.3
	20	15.1	15.3
	30	15.1	15.3
	40	15.1	15.3
	50	15.1	15.3
	60	15.1	15.3
	70	15.1	15.3
	80	15.1	15.3
	90	15.1	15.3

As a point of reference,  if you go between (2) WS-X6748-GE-TX (DFC3C) cards in a Catalyst 6500, the latency will range between 8 and 14 microseconds when tested at 90% load for similar frame sizes.