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BP1018 Sizing and Best Practices for Citrix XenDesktop with Dell EqualLogic Storage 2
2 Virtual Desktop Infrastructures
VDI helps IT organizations simplify administration and reduce costs while enhancing security and
regulatory compliance, increasing IT flexibility and business agility, and strengthening business
continuity and disaster recovery. However, a VDI deployment must be carefully designed to ensure
that it delivers the performance and scalability needed to support an enterprise-wide client
community. When moving from a distributed standalone desktop model, all components—storage,
processors, memory, and networking—are moved to a centralized data center for all the users, making
appropriate design and sizing critical to success.
A VDI deployment can place high capacity and performance demands on the storage platform. For
example, consolidating large amounts of inexpensive stand-alone desktop storage into a centralized
infrastructure can create tremendous capacity demands on expensive shared storage used in VDI
deployments. Performance demands include I/O operations per second (IOPS) generated by basic
desktop client operations such as system boot, logon and logoff, and by desktop usage operations
from different users. Typically in a VDI environment, the IOPS generated by virtual desktops are
random and can have significant impact on the storage. Storm events such as morning logons and
afternoon logoffs by many users at approximately the same time can cause I/O spikes that place high
performance demands on the storage infrastructure. There may also be situations like an unexpected
power shutdown which require booting of all the virtual desktops at the same time. This kind of I/O
storm (boot storm) creates significantly higher IOPS on the underlying storage array.
To be successful, storage designs for a VDI deployment must take these demands into account. In
particular, the storage platform should have not only the high performance and scalability required to
handle large I/O and system resources utilization spikes, but also the ability to cost-effectively handle
large capacity requirements. A VDI storage infrastructure should also be virtualization aware, so that
the virtualization layer can offload processor-intensive tasks (such as copying hundreds of virtual
machines for desktop provisioning) to the storage layer, where it can be done more efficiently.
2.1 Addressing VDI storage challenges with EqualLogic SANs
Dell EqualLogic PS Series iSCSI SANs are well suited for supporting VDI deployments because they
offer scalable, high-performance, virtualized storage designed for reliability, manageability, and
efficiency. EqualLogic SANs come with a range of efficiency features to enhance utilization and help
reduce costs. For example, automated workload tiering and load balancing help optimize storage
performance. Storage virtualization coupled with thin provisioning can provide increased capacity with
reduced physical storage requirements. EqualLogic Multipath Extension Module (MEM) for VMware
vSphere provides advanced multi-path I/O functionalities such as automatic connection load
balancing for highly available access to the EqualLogic SAN in a VDI environment. EqualLogic also
offers additional features such as thin clone technology, comprehensive integration with VMware
vStorage Application Programming Interfaces (APIs) for Array Integration (VAAI), and VMware
virtualization awareness that enable you to create more efficient deployments.
In a Citrix XenDesktop VDI solution, many virtual desktops can share the same base desktop image.
This scenario causes the data in a relatively small portion of the storage system to become extremely
hot (very high read/write I/O rates). The EqualLogic hybrid arrays – EqualLogic PS6010XVS and
PS6100XS – are designed to support fast access to high demand hot data segments. These hybrid
SANs have high performance SSD drives as well as high capacity SAS hard disk drives. When data