Today a customer told me that he couldn’t vMotion virtual machines between a few hosts, he received this warning message:
Migration to host <<unknown>> failed with error Already disconnected
An unknown error has occurred.
vMotion migration socket connected returned: Already disconnected
After some troubleshooting I’ve checked and tested:
– Same VMkernel (+ case sensitive) name;
– Same VLAN;
– Same subnet;
– Same default gateway;
– They configured unique ip-addresses;
– Host A can ping host B, vice versa;
– Ping is stable < 1 ms;
…reading KB1030267 I checked the MTU size, somebody configured the MTU size with a 9000 value at the Management / vMotion VMkernel..
The 9000 value was configured (at the hosts with the vMotion problem) but not at the physical switches, after revert to default value (1500) I was able to vMotion again, problem solved