When you copy or move the data store
location of an existing VM running on VMware vSphere you will be presented with
a message box (as seen below) in the vCenter Client asking if your VM has
either been ‘moved’ or ‘copied’. As you can see the message box also mentions
“msg.uuid.altered: This virtual machine may have been moved or copied”, but
what does this actually mean?
What is a VM’s UUID?
Firstly, it is important to have an
understanding of what a ‘UUID’ (universally unique identifier) is. As the name
suggests the UUID is a ‘identifier’ (128 bit integer) which is ‘unique’ to that
VM, and effectively gives it a digital fingerprint to differentiate it from
other VMs.
The UUID is automatically generated
when a VM is first powered on or moved, with the UUID value being based on the
physical host’s identifier and also the path to the VM’s configuration (vmx)
file. Within this configuration file the UUID value is stored in two places:
- uuid.bios
- uuid.location (hash based on the current path of the VM)
For example: uuid.bios = "56 4d
5e 58 66 f5 2d 04-03 31 0a bd 6f a7 19 88"
The UUID is also stored in the
SMBIOS system information (ie: the BIOS of the VM) descriptor. When the VM is
started or moved the location UUID (ie: uuid.location) which is hashed from the
VM’s data store path is compared to the UUID location hash which already exists
in the configuration file. At this point if the new and existing location UUID
value differs then ESX knows that the VM is now running from a different data
store location and will present the ‘Virtual Machine Message’ in figure 1
above.
We saw in the message above provided
by ESX informing that the UUID has in someway been altered but why does this
really matter? The answer to this you’ll be pleased to know is quite simple. A
VM’s unique UUID is used to generate other unique values used by the VM such as
the unique MAC (media access control) address of the network card(s). For
example if you had multiple copies of the same VM/Guest OS running in your
vSphere environment all with the same (ie: non-unique) network MAC address you
will likely receive duplicate MAC address error messages within the guest OS
which can cause a number of issues.
Another potential point to be
mindful of is that some software licensing can be linked to a MAC address of a
guest OS’s network card. This includes software such as Microsoft Windows where
changing the MAC address and some other key hardware components (eg: moving
from an Intel based ESX host to a AMD based ESX host) can mean you have to
re-activate the software again. The changing of a VM’s MAC address will occur
when you select “I copied it”, the next couple of sections will go into more
detail on what exactly is altered.
Should I Select “I Moved It” or “I Copied It”?
So what is the difference between
selecting “I_moved it” or “I_copied it”? The easiest way to demonstrate the
differences is by viewing the configuration file (vmx) for the VM before and
after the two different options have been selected.
“I Moved It”
By indicating that you had moved the
VM (instead of copying it) the only UUID change that is made to the
configuration file is to the ‘uuid.location’ setting, which as you’d expect
indicates a change of location for the VM. The ‘uuid.bios’ and the existing
generated network MAC address remains that same.
You will also notice that the CPUID
settings have also changed which is also the case for when you indicate that
the VM was copied.
The “I Moved It” option should be
used when ‘moving’ the location of where a VM resides and a copy of the VM has
not been made.
“I Copied It”
When you select that the VM has been
copied then there a few more changes that are made to the VM’s configuration
file when compared to just moving it. These changes are to the ‘uuid.bios’,
‘uuid.location’ and as a result of these changes a newly generated network MAC
address (ethernet.generatedaddress).
The “I Copied It” option should be
used when you’ve made, and intend to run, more than one copy of the VM in your
vSphere environment.
To summarise, here is a table which
outlines the changes that are made when either the “I Moved It” or “I Copied
It” are selected
As you can see it is worth spending
the time to understand the changes which will be made when presented with the
“I moved it” or “I copied it” options as it can impact (eg: software
re-activation) the guest OS of the VMware vSphere VM.
I hope this helps clarify this small
aspect of VMware vSphere administration which can sometimes be an area of
confusion.
Source:-
http://techhead.co/vmware-esx-i-moved-it-or-i-copied-it-whats-the-difference/
Source:-
http://techhead.co/vmware-esx-i-moved-it-or-i-copied-it-whats-the-difference/
