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Don’t let your VDI Storage Turn into a Horror Movie

By Alex Aizman, CTO, Nexenta.


Date: 16 Apr 2012

At first sight, desktop virtualisation looks like a great solution for many companies seeking to conquer the problem of trying to manage and maintain their PC infrastructure. What’s not to like about something that allows a business to centrally install, update, manage, maintain and secure a common desktop operating system across all its PCs and notebooks?

Things are never as simple as they first appear, however, especially with IT. Very often, making things easier at one point can add complexity somewhere else. It’s a bit like the scene in a horror film where the hero/heroine runs into a room and closes the door behind them, thinking that they’ve escaped from their pursuer only to find themselves confronted by something even worse on the other side of the door. Remember that the next time someone starts extolling the benefits of implementing a VDI (virtual desktop infrastructure) project.

OK, so it’s not quite that bad, but there are some things people need to consider and address behind the scenes. before they go ahead with any VDI implementation. One of the biggest of these issues is storage. Did you know that for every $1 spent on VDI, a company will spend from $3 to $7 on storage? Now that’s scary.

Why is that? There are a number of reasons. Consolidating many dozens and potentially hundreds of desktops onto a single server means loading the latter with small-size random I/O operations generated by all those desktops – the type of traffic that is commonly associated with “boot storms”, “login storms” and bursty random write workloads. It’s important to understand storage requirements are not just physical (in terms of gigabytes or terabytes) but are also related to IOPS.

Requirements on the storage subsystem to support hundreds and thousands of VDI desktops using Windows are very high. Boot storms, for instance, may result in several minutes, maybe longer, for virtual desktops to boot.

This highlights a number of differences between server virtualisation environments and VDI implementations. In the server environment, peak workloads are randomized among applications, in a VDI enviroments, however, peak workloads are often concurrent. Whereas in server virtualization performance fluctuations have arguably little impact as far as immediate end user experience, they can have a very profound negative effect on VDI users.

Storage in a traditional infrastructure is often loaded with a fairly sequential load, with read/write ratio at or around 80% read, 20% write. Combining hundreds of desktops in the VDI environments shifts this pattern from sequential to random with read/write ratios at 40:60 (or worse). This inevitably creates a new type of challenges for the storage software and hardware.

One way around the issue of login/boot storms and bursts of writes by desktop users is to use separate solid state disk (SSD) caching read/write operations to speed up the whole process as part of a tiered storage strategy.

In a few cases, it’s possible for companies to use their existing storage to meet the requirements for a VDI implementation. More commonly though, it is better to look for solutions and products capable of overcoming the VDI performance and cost challenges, utilizing SSDs to improve the read and write performance, normalize the I/O pattern and cost effectively meet the high-performance requirements.

The best way to avoid unpleasant surprises with VDI is to ensure that the implementation is well-planned and the right amount of storage is allocated for the deployment. Monitoring and capacity planning is important while inline compression, data deduplication and thin provisioning are technologies that can help to mitigate the costs of VDI storage.

Many of the issues surrounding VDI and how to provide the storage to support it are now out in the open and a few vendors are putting technologies in place to help mitigate any potential difficulties or bottlenecks that the shift to desktop virtualisation can bring. The good news is this particular horror film could well have a happy ending. The next time someone opens that door and close it behind them, there may well be something better on the other side.


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Tags: Desktop Virtualization

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