Bug in Cluster mem.usage.average Statistic in vSphere 4.0 U1

A while back I posted a script on a basic capacity report I run each month to get an overview of CPU and Memory usage in our various clusters. Since upgrading to vSphere 4.0 U1 I noticed some strange behavior in the results for memory, i.e. they came back at pretty close to 0% (typically between 0.05 and 0.06%) for the average memory usage in a cluster which typically were quite heavily used. On investigating further this also appeared the same in the GUI.

Using Get-Stat, mem.usage.average comes back at 0% where it should be a significant value:

The same in the GUI, the other cluster memory stats have significant values, but Memory Usage Average flatlines along the bottom of the graph:

This stat shows normal behaviour against host machines. I reported it to VMware who confirmed it to be a bug in 4.0 U1.

Thought I would share in case anyone else spends some time scratching their head and checking maths in scripts like I did. I’ll post back when there is a fix.

Update 19/05/2010:

Just got a follow up email from VMware Support that this bug will be fixed in VC 4.0 U3 - no release date for that yet.

Update 01/06/2011:

Thanks to Michael for pointing out in the comments that this is confirmed fixed in VC 4.0 U3. I make that 1 year + 1 month from the time of reporting the issue to it being resolved in an available fix :-)

http://www.vmware.com/support/vsphere4/doc/vsp_vc40_u3_rel_notes.html#resolvedissues