Q&A: Server Virtualization and Storage

Virtualization is so radically different from physical computing that entirely new approaches to storage are required. So why aren’t vendors keeping up?

Virtualization impacts many areas, but one that is often overlooked is storage. Virtualization is radically different from physical computing that entirely new approaches to storage are required. So why aren’t vendors keeping up? For answers, we turned to Mark Davis, CEO of Virsto. Earlier this year Davis' company announced Virsto One, a hypervisor-based storage solution that anticipates the demands, barriers, and opportunities native to server virtualization.

Enterprise Strategies: What unique issues does server virtualization bring to storage?

Mark Davis: Almost all storage technologies used today are based on techniques that date from the age of physical servers. Unfortunately, a number of assumptions built into such products are invalid for virtual servers. The idea that snapshot performance is not as important as for base images and that server software does a decent job of optimizing I/O are just a few assumptions made in the physical server world that do not cross over into virtual environments.

Although snapshots and clones may not be expected to live long in a physical server world, in a virtual world there are hundreds of virtual machine images that are expected to run in production for a long time. Likewise, although device drivers, volume managers, file systems, and databases have optimized the I/O streams sent to disk subsystems for decades, in a virtual world the hypervisor scrambles these streams from multiple guest VMs, resulting in significantly reduced physical server output. Because of these and many other assumptions, storage is far from optimal for virtual environments.

Virtualization is so different from physical computing that entirely new approaches to storage are required. Unfortunately, most storage vendors have taken an incremental approach to modifying dated technologies. Just as repurposing old systems from the pre-client/server era in the Internet age was fundamentally inadequate, so, too, is tweaking storage designs built on the assumptions of the physical server age.

How do these issues manifest themselves in moving from physical to virtual environments?

We hear four complaints from users of virtual servers. First, virtual servers consume up to 30 percent more disk space than physical servers. This is caused by the well-known “VM sprawl” problem. With virtualization, a server becomes a flexible software object, a big file that looks to a guest OS like a disk. Thus, VM sprawl is storage sprawl.

Second, virtual servers have unique I/O performance characteristics that don’t lend themselves to traditional storage solutions. One big problem is the “VM I/O blender”, which causes disk performance to drop as VMs are added to a box and as I/O-intensive applications are virtualized.

Third, virtual server storage management is more complex than for physical servers. Currently, it is manually intensive, takes too much administrative time, and is fraught with opportunities for mistakes. Remember, a VM is just a big file, so provisioning a VM means provisioning storage. Storage management is integral with VM management, so ideally the hypervisor would have integrated storage management.

Finally, a consistent user complaint is the total cost of VM storage. Organizations go virtual first and foremost to save money, but often all the money saved on servers is spent on extra storage. That makes no sense.

How do virtual machines (VMs) impact storage differently? How are these differences relevant to IT?

VMs drive a couple of changes in IT organizations. First, networked storage is required to take advantage of features such as VM migration. For some organizations, this means bringing in new kinds of storage systems and new staff training. Second, server administrators need to acquire more storage skills. You can’t manage a VM without having to manage storage. The role of the server administrators in managing storage becomes heightened.

In fact, a number of organizations are collapsing the server and storage admin teams because having them separate causes too much organizational friction. In the virtual world, the epicenter of datacenter management is the VM, the place where application meets infrastructure. This is causing IT organizations to realign.

How is IT addressing the storage issues they are having with server virtualization?

IT has two choices. First, be less aggressive in adopting virtualization. That is, leave more applications on physical servers and accept reduced consolidation benefits by running fewer VMs per box.

The second option is to overprovision storage. This is what most shops do. Buy more terabytes, more spindles, more I/O hardware, higher end storage arrays, more cache, and more expensive software licenses. Ironically, everyone loves virtualization because it helps us not overprovision servers, yet the only way to achieve that is to overprovision storage!

This doesn’t sound like a good set of options.

Unfortunately, although not a good set of options, they are the options that most IT shops have resigned themselves to.

What are the issues with the current solutions being used?

As discussed above, the problem is that current solutions result in storage sprawl, storage performance problems, storage management complexity, and excessive storage costs.

What that really means is that adoption of virtualization is being impeded, despite IT and its customers wanting to more aggressively go virtual.

What best practices can IT follow to address these issues?

IT definitely has options in terms of best practices. The best option is to understand the workflow at the time of implementing virtualization as a solution. Understanding workflow gives IT the ability to create projected and forecasted data center capabilities for growth and changes along with understanding the impact of not reacting to a situation soon enough.

Workflow analysis happens at multiple layers in the data center -- application, server, and data to name a few. IT environments are very dynamic and if workflow can be understood clearly, it can be modeled for setting up best practices to aid in adoption of virtualization.

How does Virsto approach the issues that storage and virtual servers bring?

At Virsto Software, we’ve built a fresh new solution that is 100 percent optimized for the unique needs of virtual servers. Our product is a small, simple software add-in to Microsoft Hyper-V that directly addresses the issues we’ve discussed. With Virsto software, the amount of storage consumed by VM images can be reduced by up to 90 percent, storage I/O performance can be improved by up to a factor of five, storage management is greatly simplified, and in the end, the total cost of storage can be cut by at least half.

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