Three key VDI storage challenges

Virtual desktops offer some attractive benefits, but storage systems that aren’t up to the task can make it hard to realize those benefits.

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Virtual desktops offer some attractive benefits, but storage systems that aren’t up to the task can make it hard to realize those benefits.

Organizations are increasingly adopting virtual desktop infrastructures (VDIs) to extend the benefits of virtualization from servers to user desktops. With VDI, each desktop is created as a virtual machine (VM) that’s centrally stored and managed in a consolidated server and storage infrastructure. VDI can provide IT managers with increased security and control, while users gain improved and more flexible access to their data and workloads.

Other promised benefits -- such as better application performance, improved data protection, and simplified provisioning and management -- have proven more elusive. By far the biggest obstacle to these benefits has been inefficient storage.

Challenge 1: Poor performance

One of the biggest VDI storage pain points is performance, which can be compromised when multiple VMs on the same server access shared physical resources at the same time. This can happen during “boot storms” when a large number of users attempt to log on simultaneously. Concurrent desktop antivirus scans (or “AV storms”) can also be a culprit because they can completely saturate shared compute and storage I/O resources.

One way to remedy the situation is to overprovision storage, but this is an expensive and at best temporary solution, as bottlenecks tend to recur as a virtual desktop infrastructure grows.

Some innovative vendors are addressing these issues with offerings tailored to the storage needs of a VDI. Nimble Storage’s CS-Series array family is one example. Nimble’s “secret sauce” is its Cache Accelerated Sequential Layout (CASL) architecture, which features inline data compression, integrated flash cache for performance, low-cost hard disk drives (HDDs) for capacity and sequential writes. A large adaptive flash cache prevents boot storms by absorbing the heavy, read-intensive I/O load, with cache reads that are some 50 times faster than disk reads. Nimble addresses AV storms through its sequential layout of writes. By coalescing random writes into a full stripe, Nimble enables write operations that are on the order of 100 times speedier than those on conventional arrays, which employ fixed layout methods.

Hewlett-Packard (HP) also has storage systems designed to meet the rigors of VDIs. The HP VirtualSystem CV2 for VMware View is built specifically for client virtualization, combining P4800 iSCSI storage-area network (SAN) storage with HP high-density BladeSystem compute nodes to create a complete VDI solution. The HP VirtualSystem CV2’s high-performance shared backplane, scale-out clustered storage technology and performance-enhancing solid-state drive (SSD) layer help mitigate boot and AV storms, even as an installation scales up to 1,000-plus users.

Challenge 2: Inefficient data protection

A second VDI storage challenge is data protection. Traditional arrays are notoriously inefficient in how they address backup, recovery and disaster recovery (DR) in a virtual desktop infrastructure, and outmoded data protection practices can exacerbate the situation. For example, many VDI users continue to back up using agent-based, third-party backup software running on VMs. Those backups are time consuming and resource intensive, and limit the number that can be done concurrently.

While some vendors have introduced copy-on-write VM snapshot capabilities to address these issues, many of the snapshot methods are constrained in terms of the space they consume and the length of time the snapshots can be retained. These limitations can compromise recovery point objectives (RPOs) and require manual management.

A handful of suppliers have developed solutions that provide efficient, rigorous and nondisruptive data protection for virtual desktops. These products share an important attribute: space efficiency. Nimble and HP both deliver VDI data protection capabilities that overcome the issues found in traditional methods. The vendors’ space economies are rooted in primary data storage optimization technologies such as thin provisioning and zero-copy clones, whose effects trickle down to secondary storage. Nimble’s in-line compression helps shrink this baseline even further.

Both Nimble and HP then enable highly efficient, point-in-time snapshots that internally share unchanged blocks. These thin snapshot technologies reduce capacity needs by upwards of 90% over traditional backup methods, and allow users to retain hundreds, and even thousands, of snapshots concurrently; in addition, backup windows can be reduced to a matter of seconds. The lightweight snapshots can easily and efficiently be wide-area network (WAN)-replicated to a remote site for DR purposes. Recovery is streamlined from hours to minutes because the restore can be based on a recent thin snapshot.

Challenge 3: Complex deployment and management

A third VDI storage problem area stems from complexity of deployment and management. Many vendors simply repurpose existing management tools and interfaces, rather than adapting them to the particular needs of a virtual desktop infrastructure. In our conversations with VDI and storage administrators, we hear many of the same complaints, such as slow and manual provisioning, limited visibility and difficulty in troubleshooting storage inefficiencies.

While these issues are often addressed as an afterthought, a few vendors have designed their products with the VDI user experience in mind. Nimble focuses on ease of evaluation and deployment, providing pre-configured and tested proof-of-concept solutions, including profiles that can be customized for whatever set of virtual desktop applications a user plans to run. The result is a single SKU purchase and a wizard-based installation process. The environment can be managed from the Nimble control console or using the VMware vCenter plug-in.

HP’s VirtualSystem CV2 is designed to streamline VDI deployment and management in Citrix, Microsoft and VMware environments. For example, HP Insight Control for VMware vCenter Server enables a single administrator to manage storage, server and network infrastructure, with visibility into all virtual desktop storage volumes; a storage wizard helps with tasks such as creating and cloning new VMs, and adding or expanding datastores.

Both vendors provide converged primary, backup and DR storage for VDIs in a single array solution, reducing Capex and simplifying management.

What this means for you

The latest generation of VDI storage products will help unlock some of the benefits that have eluded users so far. Look for solutions that have been designed to meet the specific requirements of VDI storage.  And remember that the VDI market is still in its early stages, so tread carefully by evaluating and qualifying a full VDI solution -- including compute, virtualization, networking, storage and management -- before you buy.

About the author:
Jeff Byrne is a senior analyst and consultant at Taneja Group.

This was first published in February 2012

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