XenServer – Pool Master Recovery (The Missing Part 1 to XenServer Hosts in Halted Mode)

In July of 2012 I wrote a “part 2” regarding XenServer Hosts in halted mode — however I seem to have misplaced part 1 – which I’ve rewritten after having to need to reference these steps again recently.

There are several events which can cause a XenServer Pool to become corrupt. In a recent instance of mine, the pool master was unable to communicate with the HA storage repository (SR) and fenced. I also had another instance where several shutdown unexpectedly, and the pool master was among them. Here are the steps I performed to recover the Pool Master.

  1. Work on recovering the pool, elect the server you want to become the master, and on that box run “xe pool-emergency-transition-to-master”
  2. Once that is completed, on the newly elected/transitioned master, run “xe pool-recover-slaves”
  3. Once that is complete, you should be able to run “xe host-list” and see all of your hosts listed


Based in part on information from: XenServer System Recovery Guide

Hung VM, unable to force reboot/shutdown

I have been working with a few vendor provided VM’s which run Linux. For some reason this specific set of Linux VMs do not properly respond when issuing reboot or shutdown commands when they VMs are hung. This is even true of force-shutdown. The following process works great for virtual servers that are non-responsive in a XenServer environment, after normal reboot/shutdown attempts have failed.

  1. “xe vm-list name-label={vm logical name}” to get the uuid of the VM that is hung
  2. “list_domains” to list the domain uuid’s so you can determine the domain # of the VM above by matching the uuids from this output with the uuid for your VM from the previous command.
  3. “/opt/xensource/debug/destroy_domain -domid XX” where XX is the domain number from the previous command
  4. “xe vm-reboot name-label={vm logical name} –force”



Based in part on information from: http://www.r2dtop.com/xenserver-6-virtual-machine-crash-and-hang-issue/


XenServer Virtual Disks

Unlike VMWare (ESX/ESXi), Citrix’ XenServer presents virtual hard drives over an IDE interface which is limited to 4 devices (two primary, and two slave devices), and since you also have an optical media (DVD) present, then you are limited to only 3 physical drives presented to your virtual host within Xen.

However, according to the documentation, the maximum number of disks which can be added to a Microsoft Windows VM is 7 physical drives. However, without reading the details on how to accomplish this, you will find that you can actually only add 3 physical drives from XenCenter.

To increase this, you will need to first boot the Virtual Server and install the Xen Tools, and reboot so that XenCenter detects the correct toolset is installed. At this point you will be permitted to add a second set of 4 physical drives, which will be available within Disk Management immediately. Of course you will need to go through the customary partitioning and formatting of the virtual drive.

You need to be aware of this issue as booting a migrated system without all the necessary drives attached MAY cause issues.  In some cases it COULD even prevent the server from booting.

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