One of the greatest hurdles to the adoption of new technology is skills requirement of your technical staff. Virtualisation has without a doubt been the biggest change to IT architecture in recent times. The average IT guy has just managed to get his head around Server Virtualisation and now we say – “Would you like to try another hypervisor? Same sort of functionality, it’s just going to cost you a lot less” – As I have recently found out, the most common responses are either “How different is it from VMware?” or “Do I need to understand Linux?”

When the respondent asks about VMware, reading between the lines, there is an understandable element of – “If I have to learn all this stuff over again, I would rather just hide alternatives from the Financial Director, and keep on doing what I know”. Well, there’s good news and bad news - The good news is that there is a lot more in common between VMware and XenServer than there are differences, and the bad news is that the FD either already knows that there are alternatives, or will very shortly know. Look out your Window, Microsoft has probably got a biplane and is etching Hyper-V into the heavens in sky writing. Seriously though, you can’t nowadays, and especially in this economic climate, propose a virtualisation strategy without doing a pilot with all the vendors.

On the “Do I need to understand Linux?” question, I am in the habit of saying –“if you can use Microsoft Virtual PC then you can use XenServer.” – The reason being that you do not ever need to use anything other than the happy friendly Graphical User Interface – XenCenter.  XenCenter is completely graphical and runs on your Windows based workstation. Even the Console of the Server has a GUI, reminiscent of those old DOS based GUIs (for those old enough to remember DOS). But the basic message is that even the most basic tasks can be done through a menu based system rather than the command line.

So here is the quick translation of all things VMware into XenSpeak.

XenServer Cheat sheet for a VMware engineer

VMWare Virtual Center	Citrix XenCenter
As you can see the concepts are pretty much the same some of the context menus are in slightly different places, but it’s pretty intuitive.
HA	HA
VMware uses network polling to ensure if a physical host is active	Citrix XenServer uses network polling and a quorum on iSCSI/FC to ensure a physical host is active.
If a failure is detected the VMs are restarted on random hosts, and DRS is used to load balance thereafter.	If a failure is detected the VMs are restarted across the least loaded hosts.
DRS	Workload Load Balancing
Dynamically Allocate workload across your pool of servers
VMotion	XenMotion
The first two screenshots show the respective Live Migration menus. The function is the same, quiesce the memory move it and repoint everything to be running from a different physical server – the disk stays where it is, only the contents of the memory actually move.
VMware Converter	XenConvert
P2V utilities, both include physical to virtual and virtual hard disk to virtual capabilities.
VMware Lab Manager	Citrix Lab Manager
Virtual Machine life cycle management for Lab environments.
Snapshot	Snapshot
You can take a snapshot at a VM level on either hypervisor. Citrix XenServer also has the ability to initiate a snapshot at the storage API level for certain storage - I understand VMware has also introduced something similar in vSphere 4.
ISO Store	ISO Store
ISO images stored on VMFS	ISO images stored on CIFS (Windows share) or NFS
NIC Teaming and VLANs	NIC Bonding and VLANs
VMware refers to this as teaming VMware uses virtual switches for VLANs Dedicate NIC to Service Console	Citrix refers to this as NIC bonding Citrix XenServer one attaches a VLAN to a Virtual Network Dedicate NIC to Management Interface
In both environments, more NICs are better. Separating Management traffic from Virtual Machine traffic
Storage Multipathing	Storage Multipathing
Performance Monitoring	Performance Monitoring
Active Directory Integration	Active Directory Integration

 

 

Storage Volumes

One of the biggest differences is how the two hypervisors view storage. VMware uses a proprietary file system to store Virtual Machine disks, the OS must reside on VMFS, but you can use RAW disk mappings for Database volumes for improved performance (I/O throughput). Linux LVM (Logical Volume Manager) volumes are supported as RAW disks (as well as other formats). Citrix XenServer on the other hand uses Linux LVM volumes for all disk requirements, and forgoes having a proprietary file system altogether.

VMware uses its .vmdk virtual disk format for virtual hard disks; Citrix XenServer has adopted the Microsoft .VHD format for it’s virtual hard disks. The Citrix XenServer format is interchangeable with Microsoft’s Hyper-V format.

 

Conclusion

The gist of it is that if you are comfortable with VMware, it won’t be much of a stretch for you to use those same concepts in a XenServer environment. 

  

Extra Aside

I was designing a XenServer solution with a customer last week, and we settled on a XenServer Embedded solution from HP. What I was really pleased to see is that the Embedded OS has moved from a high speed internal USB key to an SD slot on the motherboard. SD? Yes, the same format used in cameras. It’s good to see technology convergence; we have the media used in portable devices now feeding back into the server market. SD has become the fastest most robust mechanism to embed the hypervisor.

 

 

 

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