Virtualization Technology News and Information
Q&A with CEO Mark Davis: Virsto Storage Virtualization and VDI

This week, Virsto Software announced its hypervisor-based storage virtualization solution for virtual desktop deployments.   The solution supports Citrix XenDesktop and Microsoft Virtual Desktop Infrastructure operating with Microsoft Hyper-V on the back end. 

To get at the heart of things, I spoke with Mark Davis, the company's CEO, to find out more about what Virsto is up to.

VMblog: Discuss if you would some of the challenges around virtual desktops?

Virsto: In theory, the concept of virtual desktops is very attractive.  Centralizing all the data on desktops in a location that can be professionally managed on a regular basis has all sorts of advantages when it comes to management, data protection, security, etc.  But IT shops are very aware of the cost/desktop implications, and we’ve seen a number of analysts caution their clients that equipment ROI on virtual desktop projects can be elusive.

The key issue driving the costs of virtual desktop projects up that was not previously budgeted for is generally storage, and there are several aspects to this.  Because of the way physical hosts handle the I/O patterns generated by virtual desktops, significantly more storage hardware is needed to meet their performance requirements.  What we’ve seen at accounts is that this performance issue generally requires at least 30% more disk spindles than they thought they were going to need, based on their experience with storage attached to servers in the legacy client/server model.  That often translates to enough additional expenditure that virtual desktop projects get shelved.

VMblog: And how are these challenges being addressed today?

Virsto: The storage performance slowdown really catches people by surprise and hasn’t been budgeted for.  The typical first response to it is to throw more hardware at the problem.  Administrators have determined how many IOPS they need to meet their performance requirements, and so they add spindles, building up to the point where their storage configuration will actually deliver the IOPS they need for their virtual desktops.

Solid state disk (SSD) is also often considered, although you have to be a bit careful with that.  SSD has great read and sequential write performance, but does not perform well in environments with random writes.  The I/O pattern generated by virtual desktops is very random and very write intensive, and exhibits wide variability between peak and average IOPS requirements due to phenomena like boot and login storms.

VMblog: With the various solutions that are out there right now, what makes Virsto's approach unique?

Virsto: Well, we’re a pure software play that actually establishes a new virtual storage architecture that is specifically designed to resolve the unique storage issues in virtual environments, both server and desktop-based.  Virsto’s Virtual Storage Engine provides three main benefits:  it increases the IOPS/spindle on any storage, which includes storage you already own or any storage you might buy, it delivers this high performance while at the same time thin provisioning any virtual disk you may use, and it provides very scalable snapshot/clone technology that outperforms what you would get if you bought high end, enterprise-class arrays.  There’s no hardware to buy with Virsto, we’re simply a software component that plugs into the hypervisor.

Virsto offers much more compelling economics than any hardware-based solution.  At a list price of $2800 per physical host, we will increase the IOPS/spindle by up to 3x, reduce storage capacity consumption by up to 90%, and support an unlimited number of high performance snapshots without consuming any additional storage (until you start to write to them) or incurring any performance degradation.  Even in small environments with 4 or 5 physical hosts and maybe 25 total VMs, we’ve seen savings of $50,000 - $70,000 from storage hardware that people do NOT have to buy to meet their performance requirements.  Since the savings are generally in the form of the number of spindles you don’t have to buy, larger projects generate greater savings.  And in virtual desktop environments, the cost savings we generate allows shelved VDI projects to be re-started because we bring the cost/desktop back into a positive ROI range. 

VMblog: What are the fundamental differences between storage in virtual desktop versus virtual server environments?

Virsto: The basic storage problem in virtual computing environments in general is the performance slowdown.  Legacy storage architectures were really designed to perform well when you had a single I/O stream coming out of a server running a primary application.  Virtual computing changes all that, moving to a model where you have multiple VMs, each with their own individual I/O stream, that have to be handled by the hypervisor.  This generates a very random, very write-intensive I/O pattern that legacy storage architectures do not handle very well.  Because of the randomness, rotational latencies and seek times start to dominate data transfer times, and you get a lot fewer IOPS per spindle as a result.

This problem is actually worse in VDI environments.  In a virtual server environment, you may have 8 – 12 VMs per host, but in a virtual desktop project you may have 50 – 70 virtual desktops per host.  That makes the I/O pattern that the host has to handle even more random and more write-intensive.  And that I/O pattern tends to have greater variability between peak and average IOPS due to phenomena like boot and login storms.  Plus, in a virtual desktop environment, you’re dealing with many more storage objects.  You might have tens or hundreds of VMs to manage in a virtual server deployment, but you can easily have thousands of virtual desktops to manage.  This has implications for both the scalability of your management GUI and the scalability of the snapshot technology you need to handle desktop provisioning.  Note that it may be difficult to handle a 5000 desktop configuration if your snapshot technology supports only 512 snapshots.

VMblog: What types of environments are best for Virsto VDI for Hyper-V?

Virsto: Virsto VDI is specifically targeted for use in virtual desktop environments that are running on Microsoft Hyper-V back ends and using either Citrix XenDesktop or Microsoft VDI on the front end.  While our virtual server product (Virsto VSI) and our virtual desktop product (Virsto VDI) share the same Virsto Virtual Storage Engine, we’ve made changes to the management GUI on Virsto VDI to accommodate the types of uses cases common to virtual desktop environments.  In this release, we’ve added object representation models in the GUI that make it easy to graphically manage tens of thousands of objects, we’ve added new “bulk operations” options for things like create, delete, mount, and unmount that make it easy to provision very large groups of desktops from a single golden master, and we’ve added software-driven storage tiering so that you have options to configure your primary storage to get the best blend of performance and cost-effectiveness for your particular environment.


I want to again thank Mark Davis, CEO of Virsto Software, for taking time out and digging into this a bit more with us and providing us with this interesting and informative information..

Published Friday, April 08, 2011 5:33 AM by David Marshall
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