Virtual Desktop Storage Basics: The hidden costs of VDI storage

In the final segment of this four-part e-book, we uncover the known and hidden costs of VDI storage, and how those costs impact your bottom line.

Virtual desktops may make management easier, but proper planning is needed to reduce storage bottlenecks, ensure performance and accommodate growth. Storage subsystems can ease VDI deployments, whose costs can balloon if you don't follow best practices for supervision. In this final segment of a four-part e-book, we'll help you understand how VDI storage affects your bottom line.

Even though virtual desktops run as instances within a server's memory, the desktop image, applications and every single fragment of user data require storage—and that storage costs money. Any organization that contemplates a move to desktop virtualization must also understand the many costs associated with acquiring, installing, managing, maintaining and protecting their users' desktops. Below are the cost points and lesser-known implications of storage for VDI deployments.

The known costs of VDI storage
Several common storage costs demand immediate attention. There are the initial capital expenditures for the storage system, the disks and any software that supports the storage. The installation costs should also be considered -- particularly for a large storage chassis that might require specific power or cooling support from the data center. Storage also needs to be administered and managed, and tasks such as provisioning, monitoring, migration, troubleshooting and backup restoration require human involvement. These costs are present in any storage projects, but large VDI deployments can put a real bite on the capital budget.

Fortunately, VDI storage costs can also be mitigated using many of the same tactics and technologies that are brought to bear on other storage projects. For example, thin provisioning allows storage to be logically allocated without all of that disk space actually in place. Since the storage space really can’t be used by anything else once it’s allocated, but it may take considerable time to use all of the allocated space, thin provisioning is a way to defer the expense of new disks until their space is really needed.

Data deduplication can dramatically reduce storage use by removing redundant blocks and files from the storage system. In effect, only one complete copy of data is actually stored on disk -- redundant data is simply removed and redirected to the one working copy. As long as the storage system can perform data deduplication on live data in real time without significantly affecting storage performance, it can be an enormous boost to storage efficiency.

Tiered storage can also be implemented to reduce VDI storage costs. For example, golden desktop and application images that form the foundation of virtual desktops can be stored on more-expensive but higher-performance disks, while user data can be relegated to larger and less-expensive disk types. In some situations, solid-state drives (SSDs) or hybrid drives can be employed in the top tier. "You can deploy SSDs as a significant aspect of your storage tier," said Ray Lucchesi, president and founder of Silverton Consulting. "With SSDs, you'll sustain better throughput and random I/O."

Finally, reducing the scope of your VDI deployment will shrink the overall storage requirements -- also reducing the cost of VDI storage in your environment. "The majority of organizations that we work with are clearly looking just for a segment of their end users to deploy desktops to," said Mark Bowker, an analyst at Enterprise Strategy Group. He notes that organizations pursuing VDI for specific tactical reasons may shoulder the expense even when the return on investment may not make sense. Organizations planning to adopt virtual desktops must consider the needs of the user base and understand their limitations. Users who require the versatility found in traditional desktop/laptop systems may not be good candidates for virtualization, particularly if they demand frequent changes or customization.

Hidden costs of VDI storage
But organizations enamored with the promise of VDI can easily incur a variety of lesser-known costs that, if left unmanaged, can balloon storage needs (and costs). A common mistake is settling for "fat" desktops where a virtual desktop includes all of the configuration files, operating systems, applications and user data. This approach works, but it is far more storage than a virtual desktop instance actually needs. When this oversized image is multiplied by the total number of "fat" desktops and then multiplied by the additional storage needed for backups and disaster recovery, the storage requirements can easily overwhelm the purported cost benefits of VDI.

Desktop provisioning administration can also be problematic and costly. VDI makes sense only when an administrator can provision and update a large number of desktops using automated techniques such as scripts. Desktop provisioning involves creating a virtual machine, installing the OS, creating a template, customizing the template and then cloning the boot image to the production desktop on the VDI server.

It might only take 20 minutes or so to tackle these tasks manually, but multiplied by dozens or even hundreds or thousands of desktops, the administrative problems become insurmountable. Patching also requires manual processes that can be equally problematic and time-consuming. "Most people might find that the biggest cost is administration," Lucchesi said.

These two challenges can often be mitigated by creating "thin" desktops. For example, administrators can thin-provision a volume, build a golden image with an operating system and applications in a template, and then create writable snapshots to be assigned to each end user. User data is stored apart from the desktop image -- perhaps on a different storage system. The interrelated components can be used and reused without creating entirely new images, and it eliminates the manual cloning process.

Patching can also be accomplished automatically while leaving user settings and data alone. Virtualization tools such as VMware's View Composer allow administrators to make images that share virtual disks with a master image, using less storage. By comparison, VMware's View Manager streamlines and automates virtual desktop provisioning and management.

Poorly implemented storage architectures and inefficient desktop provisioning can result in poor load times and unresponsive applications, as well as costly lost productivity and angry users. Proper storage system implementation is critical for adequate disk performance under random I/O workloads and network resilience to prevent access disruptions. Storage systems with advanced caching can share desktop images from the cache, radically improving load times for users where desktop images are almost identical.

This was first published in July 2011

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