So having upgraded vCenter to 4.1 it’s now running on a different server (the v4.0 vCenter was running on a 32-bit OS).
Had previously adjusted the vpxd.cfg file to allow more simultaneous vMotion operations, as per here. On the new server, because it was a fresh install of vCenter (as per chapter 5 of the vSphere 4.1 Upgrade Guide), I therefore needed to make the change again.
On the vCenter 4.0 server I had set maxCostPerHost to 24 in the vpxd.cfg file, this gave six simultaneous vMotion operations, with any further ones being queued.
I made the same change on the new vCenter 4.1 server. Note that if running on Windows Server 2008 (inc. R2) the file is found here:
I tried putting a host into maintenance mode, but got fourteen simultaneous vMotions, plus two queued. The maths has clearly changed. on vCenter 4.0 the “cost” of a vMotion was 4, thus previously 24/4 = 6 simultaneous. However 24/14 = 1.71, which is a very strange number (at least when compared to the previous nice round number of four).
A possible explanation is that whilst the vCenter server is now v4.1, the hosts themselves are still running vSphere 4.0. So more testing required once they’re all up to v4.1 too.
Interestingly, with 2 x 1GB network links for vMotion, 14 simultaneous operations worked fine, so at the moment I’m not too fussed…