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VDI design considerations
6 Dell EMC SC Series: 3,000 VMware Horizon Linked Clone VDI Users | 4735-RA-V
1 VDI design considerations
VDI workloads are some of the most I/O-intensive workloads supported by a storage array. The exact I/O load
for VDI deployments is determined by the number of concurrent users and applications. The capacity
requirements for VDI tend to be small compared to the throughput requirements, which is especially true for
linked clone deployments.
1.1 Linked clone pools
Linked clones are commonly used in VDI deployments due to their ease of management, small footprint, and
consistency. Since a base image is used for deployment, all desktops are consistent. When upgrades are
required, a new image is deployed to upgrade virtual machines (VMs) quickly and easily.
One of the tradeoffs of linked clones is reduced customization without additional tools. To retain the ease of
management and reduced footprint, all VMs are mirrored to a base image. While persistent desktops can be
enabled, this branches the VM images and makes VM replacement more challenging.
For a large number of identical desktops, linked clones are the most efficient method and one of the most
common.
1.2 Full clones
VMware Horizon does support managed full clones. These have a much larger footprint and require individual
updating, or redeployment, upon update. They also require far more storage space. This can be offset by
deduplication, but this has a performance impact and typically cannot match the capacity savings of linked
clones.
1.3 Instant clones
VMware Horizon 7 has support for Instant Clone Technology. This feature creates VMs as needed from the
base image using vmFork technology. This creates a machine on demand from in-memory data, and writes
the data to disk as a background process. This process is fast and easy to manage but requires additional
components and configuration for a persistent user experience. This is becoming more common in VDI and
should be considered for certain scenarios.
1.4 Persistent and non-persistent desktops
Linked clone desktops can be created in a persistent manner. This allows users to save customizations to
their desktops and keep files on the desktops of their VMs. This provides users a more customized
environment but increases the cost of management. Persistent desktops cannot be replaced without a
method to retain user files and settings.
Non-persistent desktops have a far lower management cost. If a desktop becomes corrupt, there typically is
no intervention required to repair it. When a user logs out, the desktop is reset to the base image
automatically. This ensures users will always have a clean desktop to work with. However, the tradeoff is an
increased storage load. Each time a user logs out, the changes are discarded and a replacement change file
must be created. The resulting increase in I/O should be accounted for.