According to an April 2008 study by the Enterprise Management Associates (EMA), "almost three-quarters of all enterprises are now using virtualization for production applications." But while virtualization has made significant inroads into enterprise infrastructure, the EMA reports that a variety of barriers are keeping the technology from being fully utilized up to its full potential. One of the major barriers is trying to manage virtualization in complex IT environments:
"Enterprises are grappling with an average of 11 different platforms (e.g. Windows, Linux, UNIX), technologies (e.g. server, application, desktop virtualization), and vendors (e.g. VMware, Microsoft, Citrix). Only 2% of all enterprises are dealing with a simple, homogeneous virtualization environment."
Despite the challenges, many companies are discovering the advantages to using virtualization in their IT infrastructure. And many are finding that the benefits of virtualization technologies, such as storage virtualization, provide increased scalability and fault-tolerance.
An overly simplistic explanation of storage virtualization is that a logical drive acts as the proxy (or abstraction) for where the data is actually physically stored. When a client seeks to access this data, it communicates with a virtual server's virtual controller, which then directs the I/O to a vdisk (virtual disk). Why go through these extra hoops and not just access the data directly from the physical locations?
For starters, a vdisk can contain data that is actually in multiple physical locations--this is transparent to the client, to which it appears all the data is one location. Additionally, vdisks also make it much easier for multiple logical drives to co-exist on the same physical storage media, making it more effective to share and pool resources. As a company's storage needs change over time, it is relatively easy to reallocate shared resources, resize existing vdisks, and even add additional vdisks (as long as the existing physical storage capacities are capable).
| VMware ESX storage virtualization implementations|
If a physical server starts to fill up or even fail, some virtualization implementations, such as VMware ESX Server, support non-disruptive data migration. This permits data to be physically moved from one location to another, while not impacting the ability to still access that data through the vidsk. In other words, even while some of the data is being physically moved, it can still be accessed for both reads and writes. The vdisk manages the mapping of the actual physical location of the data--so that to the client, it appears that all the data being access has always been in the same place the entire time. This implementation can be applied to application servers just as easily as to file servers.
In the enterprise, virtualization is often implemented in the form of hypervisors. A Type 1 hypervisor (often referred to as bare-metal hypervisor) runs directly on the underlying hardware as its own OS, with its own kernel. A Type 2 hypervisor essentially runs as an application (or guest OS) on top of a preexisting operating system. Both Type 1 and Type hypervisors support storage virtualization, but features and implementations differ significantly from vendor to vendor.
VMware ESX Server supports non-disruptive data migration, but implementing VMware ESX Server can be an expensive proposition. Microsoft's Hyper-V technology is free if you have the right version of Microsoft Server 2008, but it doesn't yet support non-disruptive data migration. As of now, the closest Hyper-V gets is with its Quick Migration feature, which performs data migration "with minimal interruption in user access" (according to Microsoft's December 2007, "Windows Server 2008 Hyper-V" whitepaper).
Hyper-V was only just officially released two weeks ago after being in beta since December 2007. Hyper-V should be considered a "1.0" product, unlike VMware ESX Server, which has been around since 2001 and has gone through several significant iterations. For now, VMware ESX Server is considered a more robust, feature-rich virtualization solution. However, as long as Hyper-V remains free and continues to mature, it should become a stronger competitor to current market dominator, VMware ESX Server. Hyper-V is likely to increase competition and possibly force a more cost-competitive landscape (i.e., VMware might have to drop its prices).
As more corporations overcome the barriers to implementing virtualization in their IT infrastructures, the benefits of technologies such as storage virtualization will surely pay off. Storage virtualization is obviously only one aspect of the plethora of technological solutions virtualization offers (but the only virtualization-specific topic we had room to discuss in this article). But will virtualization ever become ubiquitous enough to become de rigueur in nearly all IT shops, big and small? What are your thoughts on this matter? Let us know in the comments below.
The Data Center, HotHardware's new community for IT professionals, is sponsored by Dell's Future of Storage. This article is part of our ongoing series of topics and discussions related to IT, Enterprise Storage and related storage technologies.