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Archive for September, 2012

vSphere 5.1 – Enhanced vMotion

September 24, 2012 Leave a comment

A new feature released in vSphere 5.1 is the ability to vMotion a virtual machine from one host to another, and at the same time migrate the VMs storage from one datastore to another.

This new feature is not available in the vSphere client, the newly updated Web Client must be used to access this option.

To demonstrate the feature, we have a Windows Server 2003 vm (2003-1), that is currently running on esx-1, and is located on a local datastore:

We access the enhanced vMotion option by right-clicking or accessing the Actions pull-down menu:

We select Migrate, and get the options to change host (vMotion), change datastore (Storage vMotion), and change both host and datastore (Enhanced vMotion):

After selecting to change both, as we are in a cluster, we select the destination host is in the cluster:

Now we select to other host to migrate to (esx-2):

Now we select the datastore to move to, I have selected the SharedVMs datastore:

Next we get the option to ensure that sufficient resources are available:

Finally we have a summary of the task:

And after a few moments, we see that the vm have moved over to the new host and datastore with no downtime:

As you can see it’s a really nice enhancement to vMotion/Storage vMotion.

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Hot Add

September 20, 2012 Leave a comment

Yes, I know, this feature has been around since vSphere 4, but having checked, I could not believe that I had not written a blog about it, so here it is!

Ordinarily, it is not possible to either add memory or cpus to a powered on virtual machine.  However, there is a hardware capability in a number of modern server class systems that enables the addition of physical ram and cpus whilst the server is powered on.

In order to facilitate this, the installed OS (Operating System) must be able to detect the hardware change, and make the additional resources available.

Starting with Windows Server 2003 Service Pack 1, Enterprise Edition and Datacenter Edition supports hot-add on both x64-based and Intel Itanium-based 64-bit platforms.

Windows Server 2003, Enterprise Edition and Datacenter Edition support hot-add memory on x86-based ACPI platforms only.

Linux guests using kernel version 2.6.19 or higher should also support hot-add.

References

Hot-Add Memory Support in Windows Server

Linux 2 6 19

In a virtual environment, the physical hardware does not necessarily need to support hot add, as long as the guest OS does, so we can take advantage of this feature to increase memory/cpu within the virtual machine without the need to restart it, saving valuable time.

The option to enable hot-add must be configured within the vm when it is powered off, it cannot be enabled while the vm is on:

The original memory as displayed in Windows:

After being enabled, when the vm is powered on, the memory/cpu can be increased:

Windows showing the increased memory:

As you can see Windows (or any other OS that supports hot-add) will instantly update to indicate the increased resources available.

Several blogs have previously identified this feature, with a lot indicating a potential limitation in the effectiveness of this feature.  The issue surrounds an applications’ ability to effectively support this feature as well as the OS.  If the application upon start up, identifies the amount of resource (at the time) that is available, if it does not have the ability to recheck at regular intervals, the application would never know that resources have been increased, and therefore would never be able to take advantage of the increased resources.

Whilst I totally agree with this observation, I would suggest that it would be much quicker restarting the application/service to ensure that it re-evaluates the amount of resources available than restarting the OS to add additional resources in the first place.

Therefore I would always suggest that hot-add is enabled in all virtual machines.

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