When you add a new datastore, vCenter initiates an automatic rescan on the ESX hosts in the cluster. This can create a so-called “rescan storm” with your hosts pounding away at the SAN. This can cause serious performance problems for the duration of the storm. Even if you don’t have enough hosts in a cluster to see a real problem, it’s pretty inconvenient to have to wait for each rescan when you’re trying to add 10 datastores.
To disable the automatic rescan, open your vSphere client.
1. Administration->vCenter Server
2. Settings->Advanced Settings
3. Look for “config.vpxd.filter.hostRescanFilter. If it’s not there, add it and set to false.
If it’s currently set to true, you have to edit vpxd.cfg and restart the vCenter service.
C:\Documents and Settings\All Users\Application Data\VMware\VMware VirtualCenter\vpxd.cfg, change this key to false and restart the vCenter service.
true
Doing this creates a new problem – you now have to manually force a rescan on every host.
Here is a PowerCLI one-liner to automate this process. It will perform the rescan on each host in the cluster, and only on one host at a time.
get-cluster “Production” | Get-VMHost | %{ Get-VMHostStorage $_ -RescanVMFS }