Running out of datastore disk space

If you're running out of datastore disk space, consider configuring your VMs with 100% virtual memory reservation as a short term solution. Doing so will zero the VMkernel swap file on the datastore which is equal to the amount of RAM assigned to the VM.

The good news is that this change can be made while the VM is running
The bad news is that the VMkernel swap file isn't deflated until the VM is powered off
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Enable daemons/services

Permanently enable daemons/services in the ESX Service Console with the following command (the numbers specify runlevels at which to start the daemons/services):

chkconfig --level 345 [daemon/service] on

ie.
chkconfig --level 345 snmpd on
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NFS datastores

One of the advantages to using NFS datastores in ESX(i) is that newly created VMs on the NFS storage default to creating .vmdk files in a thin format. This a type of thin provisioning and storage virtualization.
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Check your ESX host

Check your ESX host NTP offset, as well as gaining other valuable NTP daemon diagnostic information, at the Service Console with the following command:

ntpq -p

If you receive the error "ntpq: read: Connection refused", it means the NTP daemon isn't running or configured properly.
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VMware vSphere 4.0

What's New in VMware vSphere 4.0
Virtual Disk Thin Provisioning — Enables virtual machines to utilize storage space on an as-needed basis, further increasing utilization of storage for virtual environments. See the ESX Configuration Guide and the ESXi Configuration Guide http://www.vmware.com/pdf/vsphere4/r40/vsp_40_esx_server_config.pdf http://www.vmware.com/pdf/vsphere4/r40/vsp_40_esxi_server_config.pdf
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vCenter Server builds

Recent vCenter Server builds (English) and release dates
vCenter 4.0, 5/21/09, Build 162902
vCenter 2.5 Update 5, 7/10/09, Build 174768
vCenter 2.5 Update 4, 2/23/09, Build 147633
vCenter 2.5 Update 3, 10/3/08, Build 119598
vCenter 2.5 Update 2, 7/25/08, Build 104263
vCenter 2.5 Update 1, 4/10/08, Build 84767
vCenter 2.5, 12/10/07, Build 64201
See also http://bit.ly/aK8zQ
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Virtual machine

By default, when you add a virtual machine to a configuration in Lab Manager, the virtual machine is a linked clone that refers to the base disk of the virtual machine template and uses delta disks to describe the difference between the virtual machine template and the virtual machine. This amounts to a lot of disk savings but under certain conditions, linked clone performance can degrade over time.
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