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Storage Capacity Planning in a Virtual Environment

Here are some excerpts from a recent podcast I did with Todd Erickson over at You can listen to the full podcast or download it here.

How is storage capacity planning in a virtual environment different than in a physical environment?

I'd say the No. 1 thing is that things move. Tiering, capacity planning and I/O estimates have to take into account that workloads aren't static in a virtual environment. You have to think about what your best and worst case consolidation ratios are going to be. Also, storage capacity in a virtual infrastructure means both storage for the virtual machine images and the data they need. And if you're using server-hosted desktop virtualization, there's another set of considerations: what type of virtual machine images you'll need; whether you're going to use full images or clones; whether you're going to store user data separate from OS data -- all of these complicate the process of capacity trending.

What steps are required for successful virtualization capacity planning?

I encourage customers to make capacity planning a best practice. Think about how to forecast growth in number of users, in each user's personal data, in application data sets. One of the most common questions we hear people ask as their environment grows is 'How many more virtual machines can I safely add to my existing storage infrastructure?' That sounds like an easy question. But depending on how variable your workloads are, or the access patterns of your users, it can be challenging to calculate the answers.

Build a test environment, model your different operational scenarios and scale each of them to match your typical workloads. And make sure to leverage vendor materials. Those looking at Microsoft should also explore System Center's tools and best practices, including what's available in System Center Operations Manager and the performance resource optimization tools. It can help you generate useful management reports, not only for what you're using today but what you used a week ago.

What automated tools are available for virtual environment storage capacity planning?

It's important to start with the tools provided by your hypervisor vendor and the communities that have risen up around each of the leaders. VMware in particular has a lot of user-generated material that could be useful to help get an idea of your in-place utilization today, and how your utilization is growing over time. You need performance metrics that give you a snapshot over several weeks and several months, at least initially.

Storage vendors, like Dell and NetApp, deliver amazing metrics with some of their storage monitoring tools. Dell's SAN HQ for EqualLogic iSCSI SANs is one of the best capacity planning and management tools I've seen for virtual environments. It allows you to treat your storage pools the same way you treat your virtual server pools and grow them incrementally, adding more capacity to storage pools on the fly without taking the environment down.

I also like Hyper9 and Akorri's tools. Hyper9 lets you profile your current workloads for performance issues and to build reliable capacity forecasting models. The key overall is to establish your key performance indicators first. Which metrics -- capacity, throughput, headroom -- are most important to you up front, and then explore the tools that help you generate automated reports for those the easiest.


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