Calculating storage needs for VDI platforms

Virtual desktop infrastructures have shifted desktop storage from the PC back to the data center. As a result, the responsibility of storing user data, operating system data and other data elements has moved from the user to the network administrator.

Although this gives administrators more control, storing data in a data center is more expensive than storing it locally, and determining the amount of storage necessary for a given technology can be challenging.

When calculating the

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storage needs for a virtual desktop infrastructure (VDI), administrators often forget the needs of the ancillary management and backup products of the VDI ecosystem. Instead, many administrators simply figure out the size of a typical virtual hard drive (VHD) and multiply that against the number of virtual PCs. This is the simplest way to estimate storage needs, but it's ultimately incorrect and leaves no room for growth.

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A much better method is to look at all of a VDI platform's components and separate out the portions that deal with users from those that deal with deployment and management technologies.

Determining VDI storage needs
The first step is to figure out the amount of storage space needed for VDI. Determine the amount needed by the server, the hypervisor, the connection broker and all other VDI-associated components.

After calculating the storage needs for these basic elements, IT should consider the type of backup in place for VDI, business-continuity requirements and the storage needed for disaster recovery. In addition, remember that patches, upgrades and testing of new deployments also affect the amount of storage.

Some people argue that determining storage for virtual desktops is simply a mathematics exercise. However, certain unknowns like the amount of growth, the time needed for a transition and the elements external to the VDI can dynamically affect ancillary storage needs.

In addition, you need to consider the type of storage you will use. Will storage be delivered by a storage area network (SAN), or will some of the elements rely on network attached storage (NAS)? Will local server-based storage be needed as well? How will archival and backups be handled? These questions may not affect the amount of storage needed, but they can affect the cost of that storage.

Calculating VHD storage needs
Determining the storage needs for the hypervisor-delivered virtual hard drives (VHDs) is simpler than calculating VDI platform storage requirements.

Although administrators may have to address many of the same issues as with VDI, VHD storage needs can be broken down into the following formula:

VHD storage needs = (number of users) x (VHD size) + (backup and versioning requirements) + (anticipated growth)

This simplified formula provides a number that most administrators can rely on when determining basic VDI storage requirements.

Storage is relatively inexpensive today, and most administrators can afford a few miscalculations when determining platform storage needs. In addition, modern SANs make adding storage relatively easy. Regardless, it's better to err on the side of additional capacity. Storage is like closet space -- you can never have enough, and you will always find a way to fill it.

Frank Ohlhorst is an IT journalist who has also served as a network administrator and applications programmer before forming his own computer consulting firm.


This was first published in May 2010

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