Shared storage is the predominant approach for virtual desktops using virtual desktop infrastructure technology, but it comes with some cost and performance caveats.
In shared storage, all of the virtual desktop infrastructure instances, user data, user profiles and other desktop virtualization elements are retained in a single consolidated storage subsystem such as a storage area network. Every VDI server that shares the storage can access all of the desktop images and data across the data center LAN or through a dedicated storage network such as Fibre Channel.
The value of a shared storage for VDI is easy to understand. Every virtual desktop instance is hosted on a central server in the data center, so interfacing each of those VDI servers to a shared-storage architecture can be beneficial. For example, shared storage is easier to manage than direct-attached storage (DAS), where individual hard drives are installed on each server.
Shared storage allows administrators to locate and pool all of the available storage and provision new storage from that pool. By comparison, individual DAS disks are often lost or forgotten, making it difficult to determine storage capacity and usage.
In addition, shared storage such as storage area networks (SANs) allow for convenient centralized backups and snapshots of the virtual desktops. Admins can then centrally protect user desktop images and their data. Shared storage also provides much better workload migration than DAS. For example, if one server fails, the desktops can be migrated or restarted on another server connected to shared storage. This would be impossible using local disk storage.
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However, there are also drawbacks to using shared storage for VDI. First is the cost; SANs can be costly to deploy and maintain, so there is a significant capital investment to consider. Since many enterprises ready to adopt VDI already use SANs, the cost is mainly limited to adding enough storage capacity to accommodate the virtual desktop images and user data.
A more noteworthy problem is storage performance. VDI imposes demands on the network and storage infrastructure that admins must consider before deployment. A VDI server needs to access storage (over the LAN in an iSCSI or Fibre Channel over Ethernet setup), and each VDI instance incurs network traffic for video and user input tasks. These demands can result in extreme spikes in storage and network traffic.
For instance, bottlenecks could occur when a lot of users attempt to launch their desktop instances in the morning, in what is known as a "boot storm." This is why VDI deployments may need to wait for a network or storage architecture upgrade.