VM /ETC

Compared to VMware ESX Enterprise Edition, business continuity and high availability features are lacking when deploying Citrix XenServer “out of the box.” Specifically, XenServer does not have the built in equivalent to VI3’s HA feature. Also missing is a solution similar to VMware’s soon to be released Site Recovery Manager (SRM). However, Marathon Technologies and XenSource (now a division of Citrix) have worked together to develop everRun VM as a enterprise class answer to fault tolerant availability for Windows virtual machines hosted on Citrix XenServer. According to Marathon’s Director of Products, Michael Bilancieri, at a recent Atlanta “Virtualization for the Real World” event, the integrated solution will be generally available sometime in the 2008 Q2/Q3 time frame.

Quoting from the Best of VMworld (more on this award later in this post) white paper downloadable from the everRun link above:

” everRun creates a paired virtual machine environment that appears as a single virtual machine environment for both administration and application operations. The environment presents a single IP address and hostname to the application network so users never have to make client-side changes when failures occur. With everRun ComputeThru technology, protection can be configured so that component and even server failures go unnoticed. You simply keep computing through the failure, rather than failing over between servers.”

“The protected virtual machine appears and is managed just like a standard Windows server. Disk data is mirrored synchronously to redundant storage and network and server operations are protected from failure. The administrator loads and configures the application in the protected virtual machine as though it was being loaded onto a physical server and then simply walks away. There is nothing else to do!”

“Failure detection is automatic and recovery policy is embedded. There is no need to create and test complex fail over scripts. everRun works equally well with all classes of storage devices, unlike clusters that require expensive shared storage. Configuration is simple; everRun presents a single protected virtual machine to the administrator and transparently manages redundant resources for availability, removing opportunities for operator-induced errors.”

The everRun VM virtual appliance is called the everRun Availability Manager, and it is accessible and configured via a web interface. The browser based interface provides single glance access to events and status.

Although everRun VM is not clustering, it is like clustering in that it requires a shared private network between XenServer hosts. The technology is loaded as a virtual appliance on each host that monitors the VMs under it’s protection. For designs with more than 2 hosts the private network becomes a “token ring” -like network for XenServer hosts to communicate the status of VMs. The key requirement to the solution is latency of the private network.

Also unlike clustering, it should also be stressed that the everRun VM solution is application independent. All Microsoft applications are supported (yes, Exchange and SQL). Since the mirroring takes place at the VM level the application is irrelevant to the process.

The everRun VM solution can be scaled for one to many VM protection scenarios or even used as remote site disaster recovery fail over. For remote data center fail over with the previously mentioned latency requirement was recommended by Michael Bilancieri at the Atlanta event to be less than 10 ms.

There are three levels of protection for a VM offered by everRun:

1. Level 1 – High Availability (Basic fail over)
2. Level 2 – Continuous Availability (VM-level assured)
3. Level 3 – Fault Tolerance (Uninterrupted computing)

My notes and my memory from the event are unclear about the difference between Level 1 and Level 2, but “big red button” fail over (power off crash consistent recovery) like VMware ESX’s feature falls somewhere between these first 2 levels. Level 3 is live fail over like, for lack of a better example, clustering. everRun offers the ability to set the level of protection for each VM independently.

Marathon won an award in the New Technology Category from SearchServerVirtualization.com while at VMworld 2007. Interestingly, Marathon provided a demo in their booth at VMware’s conference running on XenServer. Marathon and XenSource were one of 2 winners in the category from over 100 exhibitors at VMworld.

Finally, everRun is not a solution only for XenServer. It will work with VMware ESX. everRun’s HA features can compliment or replace current VI3 HA functionality by offering separate protection to VMs, or offer an alternative to SRM as a Ethernet based solution for DR site fail over.

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