VMware vSphere Virtual Machine Live Clones Across Datacenters
Posted on 17.Feb 2010 by Ray Heffer in VMware, Virtualisation
Prior to VMware ESX 4 (vSphere) it was not possible to clone a running virtual machine to another datacenter, or to a virtual machine data store that wasn’t available on the source host. Now with VMware vSphere it is possible to clone a running virtual machine to another datacenter, even if the destination data store is not presented to the source host.
How To Fix Host Not Responding Error with VMware ESX, vSphere in vCenter
Posted on 05.Feb 2010 by Ray Heffer in VMware, Virtualisation
Virtualcenter looses connectivity to an ESX or vSphere host, and all of the virtual machines that are running on the host show as ‘disconnected’. You will also see that the host has ‘not responding’ in brackets next to it’s name.
This one is very simple to fix, as it is usually caused by the host agent service (mgmt-vmware) failing due to a dead process.
VMware ESX 3.x Snapshots
Posted on 12.Oct 2009 by Ray Heffer in VMware, VirtualisationSnapshots are a fantastic way of providing a quick and reliable method of rolling back the state of a virtual machine, should something go astray following an patch or update. VMware VCB also uses virtual machine snapshots to quiesce the VM prior to taking the backup data.
However, in larger environments where there may be tens or hundreds of VMware ESX servers, snapshots can also be a pain in the backside if there is no control over who is using them. Why? Because snapshots work by creating a delta VMDK that records the changes in blocks, a process called copy-on-write (COW). Over time the delta VMDK file will grow, and depending on the level of I/O within the VM it could grow faster on some virtual machines and not others.
The danger only presents itself if the datastore where the VMDK resides reaches it’s capacity. When this happens, virtual machines that are not thin-provisioned should continue to run with no problems, but think about these situations:
1) You have other virtual machines in the same datastore using snapshots.
2) You have one or more virtual machines on thin-provisioned disks.
3) You have powered off virtual machines, that need to be powered on.
In all of the above scenarios if the datastore is full then the affected virtual machines will be suspended (paused). Virtual machines with thick-provisioned disks will continue to operate as the VMDK already has the full allocated of storage space available. Virtual machines that are powered off, and need to be powered back on will fail as they won’t have enough disk space to create the virtual swap file.
