Windows 7 and IOPS is the most challenging, least understood and most frequently encountered resource bottleneck that stalls todays desktop virtualization projects. Many of these projects are Windows 7 migrations which are one of the key IT initiatives which are driving VDI adoption today. However, many IT organizations planning a Windows 7 migration with VDI are unaware that the combination of Windows 7 and Anti-virus more than doubles the amount of memory and IOPS required per desktop compared to Windows XP, which will significantly decrease virtual desktop density per server and will degrade virtual desktop performance. As a result, the storage architecture is often undersized for Windows 7. This leads to desktop performance and budgeting issues when more storage is required to fix the IOPS bottleneck.
In the document I have tested the IOPS resource requirements for Windows 7 in different situations giving the enterprise architect the information needed to correctly size storage for Virtual Desktop projects.
Example: A Single Windows 7 Virtual Desktop Running the Login VSI 3.0 Medium Workload
Why IOPS is Key
Delivering a good desktop experience, whether it is a physical PC or a virtual desktop, is a matter of ensuring that it has sufficient hardware resources (e.g. CPU, Memory, Storage) to run the operating system and applications of the desktop. With Physical PCs, the process is simple because each of those resources is both local to the PC and dedicated for that PC. In desktop virtualization, we are abstracting and pooling those hardware resources. With memory and CPU the pool of resources is limited to the hypervisor and the hence the physical server, which remains local to the desktop and is easily predictable and handled well by a variety of memory and CPU optimisation techniques. However, with desktop virtualization, the hard drive is moved to shared storage, this storage is then shared between hypervisors, allowing consequences to spread across the whole infrastructure. In order to deliver a consistently high performance virtual desktop experience that is equal or better than a physical PC, virtual desktops require constant access to low latency and high throughput storage.
IOPS and Scaling VDI for Production
Many IT organizations have delivered successful VDI pilot projects, only to fail as they scale the production rollout. During the pilot, the shared storage infrastructure delivers more than adequate throughput, providing excellent desktop performance. However, as the pilot transitions to production, storage infrastructure IO performance degrades as each virtual desktop makes requests of the shared storage infrastructure as if it were dedicated storage. The result is poor desktop and application performance and increasing user dissatisfaction with the virtual desktop infrastructure. With conventional VDI environments, the only way to address this degraded performance is to spread the virtual desktop load over more and more drives and storage controllers. This either increases the cost of VDI beyond the original budget or dooms the project to failure.
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