Yellow Bricks

by Duncan Epping

Everything you always wanted to know about XenMotion

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VMware isn’t the only one anymore doing that magical live migration and Citrix wants everyone to know about the ins and outs:

XenMotion is a feature of Citrix XenServer Enterprise that gives an administrator the ability to move a running virtual machine from one XenServer to another. Virtual machines can be moved from server to server without service interruption for zero-downtime server maintenance. Administrators can move running application work loads to take advantage of available compute power.

Read more at the source.

Howto: Rename a VM

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There are a couple of ways to rename a Virtual Machine, but there are two in my opinion that stand out:

  1. Shutdown the VM
  2. Rename the VM in VirtualCenter
  3. Migrate the VM and move it to another Datastore
  4. done!

And from the service console:

  1. vmware-cmd -s unregister /vmfs/volumes/datastore/vm/vmold.vmx
  2. mv /vmfs/volumes/datastore/vm-old /vmfs/volumes/datastore/vm-new
  3. cd /vmfs/volumes/datastore/vm-new
  4. vmkfstools -E vm-old.vmdk vm-new.vmdk
  5. find . -name ‘*.vmx*’ -print -exec sed -e ‘s/vm-old/vm-new/g’ {} \;
  6. mv vm-old.vmx vm-new.vmx
    for every file that hasn’t been renamed (.vmsd etc.)
  7. vmware-cmd -s register /vmfs/volumes/datastore/vm-new/vm-new.vmx
  8. done!

Distributed Power Management glitch

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I was just testing the new, but still experimental feature, Distributed Power Management. I’ve installed 3 ESX Hosts and added all of them into an HA-DRS Cluster. I enabled DPM and set the mode to manual and pressed “Generate recommendations”. I had one host with an HA failure and DPM recommend me to switch off another host. Which in this case would leave me with no host for redundancy… weird.

I’ve also witnessed that the host with two VM’s running on it was recommended for a power down, instead of the host that did not have any VM’s running.

The VMware website states:

 When resource requirements of workloads increase, DPM brings powered-down hosts back online to ensure service levels are met.

I guess having a full working HA cluster is definitely top priority to meet service level agreements, so be careful with this option and test it really well…

Xen HA clustering

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The company I work for, Ictivity, recently started testing with Xen(not Xensource!) and HA clustering. There were two case studies, one based on Suse and one based on Red Hat. Both definitely have it’s own advantages and disadvantages but it seemed promising to me. Today I noticed a blog on ONLamp.com about how to set this up. It’s a good read and gives you insight information. You can do this with open source only software so it will not get any cheaper than this. If this solution is suitable for an enterprise environment is definitely a point of discussion, but it is good to see there are more alternatives coming our way.

The idea of using virtual machines to build high available clusters is not new. Some software companies claim that virtualization is the answer to your HA problems, off course that’s not true. Yes, you can reduce downtime by migrating virtual machines to another physical machine for maintenance purposes or when you think hardware is about to fail, but if an application crashes you still need to make sure another application instance takes over the service. And by the time your hardware fails, it’s usually already too late to initiate the migration. So, for each and every application you still need to look at whether you want to have it constantly available, if you can afford the application to be down for some time, or if your users won’t mind having to relogin when one server fails.

Cool Tool: Active Directory Topology Diagrammer

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For anyone doing regular checks of Microsoft AD this tool is a must have:

With the Active Directory Topology Diagrammer tool, you can read your Active Directory structure through Microsoft ActiveX® Data Objects (ADO). The Active Directory Topology Diagrammer tool automates Microft Office Visio to draw a diagram of the Active Directory Domain topology, your Active Directory Site topology, your OU structure or your current Exchange 200X Server Organization. With the Active Directory Topology Diagrammer tool, you can also draw partial Information from your Active Directory, like only one Domain or one site. The objects are linked together, and arranged in a reasonable layout that you can later interactively work withthe objects in Microsoft Office Visio.