Storage considerations for virtual desktops

Now that virtualization has taken hold and is accepted in most companies, the question becomes what else can we do with it? The answer? Virtual desktops.

Advantages of virtual desktops

Virtual desktops allow for a company to have greater control over its resources (the desktops). The IT department, through cloning, can "build" a new desktop in minutes. The desktops can be backed up without pulling data across slow networks or requiring users to leave their workstations online. Virtual desktops also provide disaster recovery possibilities for the business's hot site.

In a normal (non-virtual) desktop environment, each workstation has a single hard drive, with all the applications installed on each workstation. Backups, usually file-based, are done over the network. You can create images of workstations and then push them out to new systems, but this either requires matching the hardware to that of the image or a special process to load the new drivers for different hardware. In cases where a remote site must be set up, you must push the image over a network connection or send it via DVD or tape to the site, then distribute it to the hardware at the remote site. That's a long process, especially for a DR site.

In a virtual desktop environment, you use servers to provide the hardware backbone. The servers run multiple virtual desktops (with many users sharing the same hardware). These desktops can be copied or cloned and turned into new desktops in minutes. Since virtual desktops use special virtual drives, there's no process needed for matching hardware drivers. The virtual desktop files can be a part of a server disaster recovery plan, so that when you need to turn on a DR site, the desktops are ready. There's no special hardware requirement at the remote site.  

Some drawbacks

While a virtual desktop environment provides advantages, there are things to consider when it comes to storage. They are:

  • Drive type. In choosing the drive type, the two factors you should consider are price and speed (I/O per second). SATA is generally the cheapest, but has the lowest I/O per second, at an average of 80. Fibre Channel and SAS are the faster of the drives at an average of 180 I/Os per second, but cost more per GB. Since the virtual desktops will share drives, there will be more I/O per drive than in a typical desktop.
  • Drive protection type. You would not normally use RAID in desktops, but for server class devices, it's standard since the desktops will be virtualized and multiple desktops will share hardware. RAID provides drive-failure protection that doesn't exist on standard desktops. It also increases the I/O per desktop, since multiple disks can perform the work. Any type of RAID is better than nothing, but RAID 5 would be best for most environments.
  • Drive location. Should you keep the drives locally to each server or should you use a central storage solution? In the case of desktop virtualization, central storage is a great advantage. You can combine more disks in a RAID group, thus increasing the I/O that can be applied to groups of virtual desktops. Central storage also provides a hardware failure protection should a server hosting the virtual desktops fail. And it generally has its own tools for replicating data to another device. Virtual desktops on central (shared) storage can be replicated to a remote site where they will be waiting to be turned on and accessed in case of an emergency.

To build the storage for a virtual desktop environment, it's a good idea to collect performance statistics of physical desktops and crunch the numbers to determine the right drive design for virtual desktops. The disk I/O, the number of desktops, and the RAID group type should be factors in the equation to build the right storage environment for virtual desktops.

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