Perhaps the biggest hidden cost in hosted VDI desktops, one of the four desktop delivery models supported in XenDesktop, is the requirement for high-performance storage. This isn’t an issue of capacity, it’s IOPS or the ability to read and write small bits of data very quickly which requires rock solid storage infrastructure and lots of spindles or increasingly, SDD (Flash drives). Many customers will start a pilot deployment and can pretty easily get their first 20, 50, and maybe a few hundred desktops on their virtual storage infrastructure and then hit a wall sending them shopping for a whole new class of storage that ultimately slows down the project as the calculators come out.
XenDesktop 5, Service Pack 1 now supports XenServer IntelliCache(XenServer 5.6 SP2), a new feature that (just like it sounds) intelligently caches virtual desktop storage on local SSD storage in the host. By caching locally, up to 99% of the reads and writes of the virtual desktop within the host server rather than out over the storage network, the IOPS requirements of the storage network are cut by half – which could be as much as a third of the total deployment cost of a virtual desktop.
The idea of utilizing high performance local SSD to boost performance and cut costs is not unique to XenDesktop, but the flexibility and ease of management is. The Tiered storage concept from competitors relies on cutting up your virtual desktop deployment across diskstores, permanently placing some portions on shared storage and some assigned to specific local stores. This requires careful pre-planning, and then limits the future flexibility of the deployment making it impractical for many deployments. Tiered storage is also only applicable to shared or pooled desktops.
Utilizing IntelliCache is simple, requires no planning, and is flexible – allowing administrators to live migrate virtual machines across hosts as needed. Simply enable IntelliCache when installing the XenServer hypervisor on their hosts. Then as new desktop catalogs are created with Desktop Studio, simply check the “Use IntelliCache” box and that’s it. Management remains completely centralized and no further optimization is needed.
Also unique to XenDesktop is the ability to get the benefits of thin provisioning and IntelliCache with persistent / assigned virtual desktops. XenDesktop 5 with Machine Creation Services (MCS), built right into Desktop Studio, can use the same master image to thin provision both shared/pooled and persistent/assigned VMs. While you lose some of the benefits of single image management with persistent desktops, you still pickup performance and cost benefits in virtual infrastructure. Either way, XenDesktop 5 creates a flexible, easy to use platform that enables you to deploy a wide range of desktop scenarios with common infrastructure.