Crucial Paradigm

One thing you notice online when working in virtualization is the lack of resource explaining the engines / drive trains / gear boxes what go into making system virtualization possible.

This actually goes for a lot of things, there will always be more howto’s on technical webserver stuff for linux than for windows… etc etc.

Today I am going to explain a bit about the relationship between processes and objects that come together to make your virtual machine work.

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If you have ever had problems with time on a cluster, and had trouble getting the licenses in sync in Citrix XenServer 5.6 FP1, you can run the following commend to disable HA:

xe host-emergency-ha-disable force=true

You can use the following commands to change the Citrix XenServer pool’s master server:

First you need to disable high availibility:

xe pool-ha-disable

Then you need to find out which host you want to change the master to:

xe host-list

Then change the master:

xe pool-designate-new-master host-uuid=[uuid of new master host]

Turn HA back on:

xe pool-ha-enable

Sometimes when shutting down a VM via the standard XenCenter interface or command line (xe) on a Citrix XenServer machine the shutdown will not complete.  The first thing to try is a force shutdown on the VM:

xe vm-shutdown –force vm=[vm name]

If this still doesn’t work you can try taking a look in the XenServer pending task queue:

xe task-list

And cancel the process’ that seem to be holding up the system:

xe task-cancel uuid=[task uuid]

If this still fails you can try the following:

xe-toolstack-restart

If you have noticed your Citrix XenServer machine grind to a halt due a process “cdrommon” this is a known bug with a particular CD-ROM drive in XenServer.  A fix for the bug can be found here:

http://support.citrix.com/article/CTX126919

In short to check if you are effected by the bug, run the following:

dmesg | grep DV-28

This bug applies to “TEAC DV-28E-V” CD-ROm drives.

Adding a local storage repository to a Citrix XenServer 5.x server can be done as follows:

NOTE: Extra precaution should be taken while using the following commands, as it could result in data loss.  Only perform these steps if you know what you are doing:

1. Locate the disk ID by using the following command:
   # ls -al /dev/disk/by-id
2. Create the local storage repository:
   # xe sr-create content-type=user device-config:device=/dev/disk/by-id/<scsi-xxxxxxxxxxxxxxxxxxxxxxxxx> name-label=”Local Storage X” shared=false type=lvm

If you ever wondered how to remove the physical NIC configuration on a Citrix XenServer machine, this is how you can do it:

xe pif-reconfigure-ip uuid=XXXXXXXXXXX mode=none

Where “XXXXXXXXXXX” is the uuid of the NIC to remove the configuration from, this can be either a NIC or a bond.  To find out the NIC/bond uuid you can run the following command:

xe pif-list

If the physical interface used for the manage interface needs to be changed, edit the MANAGEMENT_INTERFACE field /etc/xensource-inventory file on the host to reflect the new interface being used. Make sure you use the bridge interface (e.g. xenbr0) and not the physical NIC.

Once you have made this modification you will need to run the following:

xe-toolstack-restart