Thursday, November 5, 2015

VSAN 5.5 - Verifying jumbo frames

I've been working on a Virtual SAN 5.5 POC (for various reasons, the environment is still on vSphere 5.5u2) and came across an issue following the guide provided by VMware:

Tips for a Successful Virtual SAN 5.5 Evaluation

It states on page 9 to use vmkping -S 9000 to test connectivity between hosts using jumbo frames.

There is where I hit a wall....  I kept getting the following error message:

~ # vmkping -S 9000
*** vmkernel stack not configured ***

I kept racking my brain, checking my configuration, making sure that MTU 9000 was set on the distributed switch and also on the VSAN VMkernel, and that my network switches were set to support jumbo frames on both the physical ports and on my VSAN VLAN (I use VLAN 1001 since VLAN 1000 is my vMotion network).  Then I came across the following post:

Even though that is an old post from well before VSAN existed, it is still entirely relevant.  Now armed with the correct formatting of the command:

~ # vmkping -I vmk2 -s 8972 -d
PING ( 8972 data bytes
8980 bytes from icmp_seq=0 ttl=64 time=0.176 ms
8980 bytes from icmp_seq=1 ttl=64 time=0.159 ms
8980 bytes from icmp_seq=2 ttl=64 time=0.157 ms

--- ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.157/0.164/0.176 ms

Eureka!  (also vmk2 is my VSAN VMkernel interface and adding "-I vmk2" specifies what interface to force the ping to travel over)

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