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Migrating an entire virtual data center isn't something administrators think about often or wish to undertake. However, the need does arise occasionally. Recently, I had to migrate an entire virtualized data center from one physical location to another.
The most important thing you can do is plan ahead. There tends to be a large disconnect between what management expects and what an administrator can reasonably deliver. An administrator can only migrate a certain number of machines in a given time period. All but the smallest estates will require multiple days of migration. As such, a properly defined virtual data center migration plan with a list of machines will make your life much easier.
Develop a step-by-step migration plan
Focus on key infrastructure first. When considering which servers to migrate, don't forget to group the application stacks together so all the applications end up at the right side of the wide-area network during the migration.
Don't try to move the old environment's management infrastructure in the new environment. Take a detailed inventory and leave no stone unturned.
One item I found useful was to see if machines were actually in use. VM sprawl can easily take over in a poorly managed environment. There is no point in migrating unused machines that are burning licensing and resources that the new environment will never use.
Look at the traffic first, if you're unsure where to start. Does the VM register activity over an extended period? What about disk I/O? You can also use system logs to determine if the system is still in use -- login times, HTTP stats and so on. This troubleshooting will help find machines that may be grossly over-specified or unused machines you could potentially reclaim.
I would also suggest using this opportunity to install and configure a new virtual management infrastructure, such as vSphere or Hyper-V. Admittedly, it will need hardware and at least some temporary licenses, but it gives you control over the environment and reassurance things are working as they should.
Using this approach for your virtual data center migration plan not only allows you to fix any errors in the old implementation, it also provides you with a solid staging point to migrate to. This way, you'll avoid blind panic trying to get key infrastructure up and configured during the migration. Not preseeding the estate and trying to sort this on the fly will result in a great deal of stress and potential errors.
Most platform vendors have tools that allow you to back up and restore virtual folders, settings and configurations to a new environment.
Make sure that key supporting infrastructure is ready and available prior to implementing any virtual data center migration plan. You should identify key infrastructure components, including time servers, Active Directory, domain name systems and so on. A smart administrator won't attempt to migrate the entire key infrastructure at once, but will have synchronized copies at each location that can be removed from the old site once everything is proven to work correctly. You always need a backup plan in case things don't go well.
Simplify your approach with automation
Make your life easier by automating the migration. Performing anything but the smallest of migrations with manual tools is a form of insanity. When you are attempting to migrate dozens of machines in a constrained timeframe, trying to use the hypervisor vendor's tool of choice will be painful and ridden with problems -- or even worse, it will require manual copying across the wide-area network. That is a lot of waiting around, and there are just too many potential areas for failure.
There are useful tools that allow you to preconfigure VMs and migrate them with very little downtime because they can synchronize over a longer period. Also, when it's time to cut over, only a minimal amount of data must be replicated. There are several vendors of such software, including Zerto and Veeam.
The beauty is you can plan it down to the minute and have the VM at the new site up and running with the IP and domain name system information you potentially configured several weeks ago. It takes the pressure off and allows time to make sure all the details involved in your virtual data center migration plan are correct. Compare and contrast this with some manual tools. If budget allows, these tools are very useful.
To put the automation into context, I was able to fail over a VM in excess of 1 TB to the new site and have it working within 10 minutes. However, I did have to allow the machine to populate and sync between the sites ahead of time.
Setting up all the configuration items beforehand brings massive efficiencies. Thanks to these preparations, it's now possible to migrate tens of machines in a single day, without maxing out the wide-area network during a copy operation.
Additional considerations for migration
One thing only administrators would recognize is you need lots of disk space. As you copy and move data around, you will find you never have quite enough.
Other items of note require a bit of common sense. If you have a VM that has performance issues, fix them before you migrate. If you migrate a poorly performing machine to a new data center, odds are the performance will be just as poor.
You need to have a verification list. When you migrate dozens of machines, there will be failures. Identifying and remediating these failures is important. For each VM, have a list of steps to verify the correct operation of the machine. In addition, get people to sign off that the application is working.
In short, there are many ways to help ensure the virtual data center migration plan is successfully executed. There will inevitably be a cost. Any business that tries to do a migration with little to no funding stands a significant chance of encountering problems. Be careful, thorough and use the functionality available to you, and you should be able to complete the migration with minimal issues.
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