After an upgrade of VMware 4.1 to VMware vSphere 5.1 Update 1 one of my colleagues Wilbert Kandt noticed that the environment wasn’t properly load balanced. The problem was that an ESXi host wasn’t used as destination within a VMware DRS cluster after a while.
After some investigation it became clear that the CPU and memory usage of the ESXi host wasn’t shown in vCenter.
When the vCenter Client was used to make a direct connection to the host the CPU and memory usage was displayed correctly. So it was save to say the problem was the latest upgrade of vCenter and it had something to do with the communication between the management agent en vCenter.
Because of this issue the load isn’t indexed correctly thus DRS isn’t able to do its job because there’s no reported load which can cause performance issues and disruptions for the end user.
This behavior was caused by a bug in vCenter Server and this bug is in the following versions of vCenter:
- 5.1 (799731),
- 5.1.0a (880471),
- 5.1.0b (947939)
The solution was pretty easy, vCenter had to be upgraded to the lastest version: vCenter Server 5.1 Update 1. (5.1.U1-1065152)
If you’re not able to upgrade vCenter there’s a temporary workaround by restarting the VMware Management agents which restores the connection between the ESXi host and vCenter. There’s an KB article describing how you can restart the agents: 1003490 and it includes a small video demonstrating how you can do this too. Please keep VMware HA and Autostartup list in mind when restarting the agents.
I can’t stress the fact that if you’re going to do an upgrade (of any product that is) you should always read the release notes and the known issues so you can decide impact and always ALWAYS have a rollback scenario.
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