Unable to Migrate / Start / Shutdown VM (Virtual Machine) Dead Beef 

This is a not so common scenario when you try to destroy domain for a VM using following command 

#/opt/xensource/debug/xenops destroy_domain -domid 140

and then you'll see "VM stuck in dying state" in logs and following in list_domains 

Now to the solution :

Scenario 1: You have multiple VMs running on that server :

In this case you'll have to RDP to all machines and turn them down individually. Then you'll have to reboot your XenServer host to fix the server. This error won't let you shutdown VMs from Xen Center/CLI because XenServer is not able to communicate via XAPI (Xen API).

Scenario 2: You do not have anything running on that server

Reboot your server and the issue is resolved.

Storage Assignment failed (Invalid host name or IP address, DNS lookup failed)

This error message occurs when you’re using XenServer 5.x with Storage link gateway. The host & SAN communication is good but somehow storage link management server is unable to resolve the name of destination host (Host where you want to start VM)

To troubleshoot this issue, make sure that hostname in Storage link server and the hostname in XenServer CLI is same and it is not called hostname or localhost.

There were no available servers to start VM

While booting your VM (Virtual Machine) if you come across this error, this means that either your host has run out of memory or the VM template is looking for more memory than available.

Scenario 1: XenServer is out of Memory:

Go To Search Tab for XenServer and see if that host has sufficient resources. If yes, then move to scenario 2 else get some memory resource.

Scenario 2: VM Template is looking for memory than allocated

1.       Select your Virtual Machine

2.       Right Click on it and go to its properties

3.       Move down to last option called “Advanced Options “.

 

4.       It would say “Optimize manually” and would have some random number as its value.

5.       Select optimize for general use.

6.       Click OK

7.       Boot your VM. It will boot without any issue.