Virtual Desktops are expensive to deploy from a storage perspective. With the advancements in deduplication technology the footprint of a virtual desktop deployment on storage has been dramatically reduced. The issue is no longer the cost of ‘space’ alone. Deduplication removes the ‘like’ blocks and stores just one copy and references the dependent data to reduce the amount stored. In a virtual desktop environment that consists of 100s if not 1000s of copies of a Windows desktop operating system the consolidation of storage is very high. However, the IO required for a single VM can also be high; in production VMs have been observed to require 25 – 100 IOPs per virtual desktop. While the storage footprint is small the performance requirement is extremely high. The performance footprint of a virtual desktop environment can vastly exceed the performance demanded of all but a very few high performance high demand enterprise software solutions such as Oracle, SQL and large Microsoft Exchange environments.
View Storage Accelerator
VMware has introduced several technologies that increase performance while reducing cost. VMware implemented View Storage Acceleration (VSA) which is a form of local host caching. When a virtual machine is deployed a digest file is created which references the most common blocks of the VMs operating system. In operation the digest file is used to pull the requested blocks into memory on the ESXi host. This reduces the read requests that are serviced by the storage system by introducing a host based cache.
vSphere Flash Read Cache
vSphere 5.5 introduced the capability of pooling locally installed SSDs on the vSphere hosts into a logical cache accelerator that all read intensive VMs can benefit from. The vSphere Flash Read Cache aggregates all read requests so that they are cached locally on an SSD drive vs. in memory as is the case with VSA. This creates a separate caching layer across all hosts (provided they have local SSDs installed) to accelerate performance. While not specifically designed for virtual desktop environments, it will enhance any read activity across the virtual desktop compute cluster.
View Composer, Stateless Desktops and Storage Reclaim
VMware Horizon View enables the deployment of a stateless desktop. A stateless desktop essentially redirects the writes so that the majority of the desktop is read only. A stateless desktop is a much cheaper desktop to deliver and manage operationally. This is because it is not customized to an individual user and makes use of View Composer linked clone technology. Composer enables a large number of desktops to use very little space. The decoupling between the user and desktop and use of Composer allows more flexible deployment options. Stateless desktops can make use of local Solid State Drives on the ESXi host to deploy the OS disk of the VM. The benefits have been somewhat difficult to realize though as operationally the OS disk must be recreated to reclaim unused space and reduce the size of the tree.
VMware View 5.3 introduced a reclaim process that allows this to be done automatically and to take place outside production times. This enables a linked clone tree to be deployed for an extensive period of time and reduces the manual operational process of reclaiming space. In a virtual desktop environment the predominant use of stateless desktops dramatically reduces the cost of the solution.
vSAN
VMware has entered the storage virtualization market with the release of VMware vSAN. A vSAN allows the customer to completely segregate the virtual desktop environment onto a SAN that is built using local SSD and Host Hard drives (HHDs) that are collected and presented logically as a single shared storage environment. Segregation or separation of the virtual desktop environment provides the benefit of isolating the View requirements on a distinct set of physical resources so that there is no overlap at the hypervisor or storage levels for production enterprise workloads. The benefits of this approach are many:
1. Predictive hardware performance
2. No risk of virtual desktop performance impacting general Storage performance
3. Scalable, building block approach to deployment
4. Centralized Storage through logical SAN presentation
5. Native vSphere HA enabled through point (4)
6. Reducing the cost of storage while still providing all the benefits of a SAN
The solution is based on Micro Converged Infrastructure in which a physical server with local SSDs and HHDs runs the vSphere ESXi and a storage controller as shown in figure 1. For storage controllers that support pass through, vSAN takes complete control of the SSDs and HHDs attached to the storage controller. RAID0 mode is used for storage controllers that do not support pass through . This essentially creates a single drive RAID0 set using the storage controller which requires you to manually mark the SSDs within vSphere.
VMware recently announced the bundling of vSAN as part of VMware Horizon Suite. VMware Horizon Suite includes View, Workspace and Mirage and now vSAN as well. The innovation and combination of technologies at the infrastructure layer provide additional value over and above what is incorporated into the VMware Horizon View software delivering compelling value to VMware’s customers.
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