Q

How do I calculate VDI storage needs?

Your VDI storage needs will vary depending on the kinds of desktops and images you're planning to deploy, but calculating how much storage you need is easy.

Calculating VDI storage needs has to take in a couple of variables, including whether you use persistent or nonpersistent desktops, and full or snapshot-based images.

When a virtual desktop infrastructure (VDI) session is persistent, the data for that session is kept around after the user logs off. But in a nonpersistent session, the user's data is deleted on logoff. A snapshot-based desktop shares the master image's disk in read-only mode, whereas a full image desktop is a copy of a master desktop configuration that shares no storage with the original. Both of these things affect VDI storage needs, and the various configurations all have different storage requirements. (All calculation methods below assume that you offload user profiles to central storage.)

Persistent snapshot: Snapshot-based desktops that are persistent will probably refresh often, so performance is the main concern. Write operations can range from 15 IOPS per desktop to more than 100, depending on the workload, so consider using a sizing tool and some kind of storage enhancement technology, such as flash. Calculate storage needs by multiplying the size of the master image OS disk by the percentage of growth you expect from each desktop, and multiply that by the number of desktops you need. Because user profiles are persistent, they can take advantage of deduplication-based storage arrays, but you need to account for the storage needs for those profiles: the size of each profile times the number of users.

Persistent full image: A persistent full image desktop won't refresh as often as a snapshot image does, so you can calculate storage needs by multiplying the disk size of the master image OS by the number of desktops you have to deploy. As with persistent snapshots, you'll also have to calculate the space you need to store user profiles.

Nonpersistent snapshot: Just like with persistent snapshot desktop images, nonpersistent snapshots will refresh often. You can calculate their storage needs the same way you would for persistent snapshots -- disk size of the master OS times expected growth of each desktop times number of desktops -- but leave out profile storage. Because user profiles aren't saved at logoff, you don't need additional storage for them.

Nonpersistent full image: Full images don't get recycled often, but nonpersistent desktops need to be refreshed often, so this configuration doesn't have very many use cases. If you want to deploy nonpersistent full images, calculate storage needs the same way you would persistent full images -- disk size of the master OS multiplied by number of desktops -- but leave out the profile storage requirements.

Next Steps

What are the differences between persistent and nonpersistent VDI?

Images and snapshots aren't the same

This was first published in July 2014

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