How should IT handle VDI storage sizing?
It is very easy to assume that the space required for VDI deployments is simply a calculation of the number of desktops multiplied by their capacities. In reality, things are more complex than this. VDI implementations use a master desktop image, which is cloned as snapshots or using features such as VMware linked clones. As desktops are used, the data within each virtual desktop will change, and so the overall storage requirements go up. In stateless VDI deployments this change data will be very small, and so the overall storage requirement will be the size of the master plus an incremental amount per individual virtual desktop itself -- for example, 5% or less additional storage per desktop. In addition to this space, storage will be needed for growth, maintaining and rolling out patches, and backup. Customers should also consider the additional files required to support each virtual desktop, including logs and files for RAM images.
The starting point for VDI storage sizing should be based on a typical desktop deployment -- for example, Windows XP, Windows Vista or Windows 7. Each will have different storage requirements, and typically the initial size of the boot disk increases with each operating system release. Where applications are deployed locally, the size of the boot disk (or separate application disk if one is used) will need to be increased in line with each product being deployed. Where application virtualization (for example, Microsoft App-V) is used, separate space will be required to manage the applications for all desktops, with only a minimal additional amount of storage required for each desktop.
Consideration needs to be given to user data. If the deployment is stateless, storage can be deployed on a separate infrastructure and accessed via SMB/CIFS. This separates the sizing and management from VDI planning. If user data will be provided with the virtual desktop, in a persistent desktop setup, then an initial capacity per user (with growth estimates) needs to be included into the calculations for each desktop.
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