Unlocking Citrix Xensever Memory

Wow... Has it been that long since I posted? Yeah, its been a wild few weeks, what with hurricanes, earthquakes, hail storms, trying to sell a piece of underwater real-estate at a 30% loss. Whew! But hey, here's a Xenserver hack for you:

I loaded Xenserver 6 Beta on a cluster of servers, and was disappointed to find that they had moved memory management out of the "free" product and into one of the "pay" tiers. This means that if you want to change an VMs memory reallocation, you have to pay an extra licensing fee. Silly. Especially since it was so easy to bypass.

Create a template from a VM. Log into the Xenserver console via SSH as root. Using the template name that appears in XenCenter:

# xe template-list name-label=a-Windows_Vista_x86-x2
uuid ( RO) : 4c<snip>28
name-label ( RW): a-Windows_Vista_x86-x2
name-description ( RW): SP2, Registered

What we need is the UID. View the template parameters:

# xe template-param-list uuid=4c<snip>28

Here, look for the min/max lines:

memory-static-max ( RW): 1073741824
memory-dynamic-max ( RW): 1073741824
memory-dynamic-min ( RW): 1073741824
memory-static-min ( RW): 1073741824

I this case, the template will create a VM can only be 1G... never more... never less.

Lets change the bottom value:

# xe template-param-set uuid=4c<snip>28 memory-static-min=1
# xe template-param-list uuid=4c<snip>28 | grep " mem.*-m"
memory-static-max ( RW): 1073741824
memory-dynamic-max ( RW): 1073741824
memory-dynamic-min ( RW): 1073741824
memory-static-min ( RW): 1

I haven't figured out the other three values, as any attempt to change them throws an error saying they must all be equal. They do form the top limit, but once you strip out all that Aeroglass crap and disable half the services, Vista runs just fine at less than 512Mb. But just for the record, I wouldn't suggest you try to run Vista on 1 byte of memory.