I got a tip from Chris Wahl’s blog the other day that will really helped during the vSphere 5.1 host upgrade. Beyond the upgrade, there are times when I need to work on a DRS clustered host when it’s in and out of maintenance mode. The problem is DRS, when in Fully Automated Mode, will start moving virtual machines back on the host when it emerges from maintenance mode and becomes available.
There a couple of ways around this:
– Change the DRS Cluster to Manual or Partially Automated which gives you control over virtual machine migrations, just not virtual machine placement when they’re powered on.
– Turn DRS off. This will hurt if your have resource pools because you’ll lose them.
– Remove the host from the cluster. This will require you to move the host back into the cluster and reconfigure for HA.
All of those options involve preparing and recovering from host maintenance. If you need to stop automatic migrations for a while as you work on a clustered host , use the Conservative option in the cluster’s DRS options:
The conservative setting only allows DRS to follow any DRS based rules that you have put in place. It will make no resource constraint based decisions. This has worked very well for upgrading firmware or just testing the 5.1 upgrades on the hosts.
Once you’re done messing with the host, go back into the cluster’s settings and drag the slider where you want. This is a helluva lot better than manually migrating machines.