IT must take a variety of factors into account during the VDI planning process, and storage is one of the most crucial components.
IT should think of VDI storage in terms of three broad categories: storage technologies, system requirements and supported workloads. Here, we'll discuss how each category can affect VDI planning.
The system requirements for VDI storage depend on how IT implements the VDI components and desktops. For example, most VDI vendors support both persistent and nonpersistent desktops. Persistent desktops maintain user data and settings from one session to the next; nonpersistent desktops do not. As a result, persistent desktops require more storage capacity for both the primary data and backups.
IT should review the individual features available in virtual desktop infrastructure products to determine how they affect VDI storage requirements. For example, VMware offers vSAN, a software-defined storage platform integrated into vSphere. VSAN virtualizes the local physical storage in a vSphere cluster to create a distributed shared storage product that can simplify management and help reduce storage costs.
VMware also offers View Storage Accelerator to reduce IOPS requirements, View SE Sparse disk to reclaim storage capacity and Virtual Volumes to better control storage-related operations. In addition, VMware supports desktop cloning, which enables administrators to create full or linked desktop clones from a master image. Cloning can reduce overall capacity needs, but it can also lead to write amplification issues and increase I/O requirements, especially with persistent desktops.
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Most vendors offer features that can affect VDI storage requirements and the overall VDI, usually with the intent of improving performance and resource utilization. Citrix, for example, provides Machine Creation Services and Provisioning Services, both of which can help deliver better storage performance and reduce storage requirements for each virtual machine.
IT should also evaluate the VDI storage requirements for implementing the product's components, as well as the storage resources necessary to support backups, site-to-site replication and disaster recovery operations.
For example, when planning a Citrix implementation, IT needs to estimate Microsoft SQL Server database requirements and take into account the database and transaction log files for the three primary databases -- monitoring, site configuration and configuration logging -- as well as the temporary database (tempdb). IT also needs to provide storage to back up those databases and ensure their continuous availability.
Choosing a storage product
Storage technology includes everything from drive types to storage configurations to transport protocols. For example, when planning storage, IT can choose hard disk drives (HDDs), solid-state drives (SSDs) or hybrid systems that combine the two.
HDDs were once used almost exclusively for VDI, but SSDs are quickly becoming the drives of choice because they significantly outperform HDDs. In addition, SSD densities have been steadily increasing as prices decrease, making the all-flash array a more viable option than ever. In some situations, however, hybrid storage can adequately support VDI workloads and bring prices down even more.
The final piece of the storage puzzle is perhaps the most important: understanding the workloads that the VDI must be able to support. IT should evaluate the types of users connecting to desktops, how and when those users work, and anything else about their behavior that can inform storage planning. For example, productivity workers generally have lower IOPS requirements than knowledge workers, who have higher performance requirements and use resource-intensive applications.
As part of their calculations, IT teams should determine the number of users and number of desktops they require, which are not necessarily the same. Teams should also determine how much user data they will store, which guest operating systems will run, the types of applications users will require and any other special performance or storage requirements for them to carry out day-to-day operations.
IT must ensure that storage drives can deliver the required IOPS to support the expected VDI workloads, which are typically random and fluctuate depending on the time of day, number of users and the supported applications. The calculations should include both existing and future needs, accounting for factors such as expected growth and the influx of temporary workers. IT should also account for anticipated boot and login storms or other situations that can result in high I/O demands.
Different types of drives provide different levels of IOPS, and even drives of the same type can vary substantially when it comes to performance. For example, SSDs generally deliver much higher IOPS than HDDs, but not all SSDs are created equally. IT must evaluate SSDs carefully to ensure that they can meet the expected demand.
Other VDI storage considerations can also affect user experience. For instance, server-side caching can reduce I/O latency. IT can select RAID levels to match workloads and use tiering to improve response times for virtual desktop components that need to load more quickly. The effectiveness of the array management software can also make a difference when it comes to maximizing I/O. In addition, some technologies such as deduplication or thin provisioning can improve resource utilization, but they can also potentially affect user experience.
Deployment and configuration considerations
Another important VDI storage factor is how IT configures or deploys the storage. IT must determine whether to use direct-attached storage (DAS), network-attached storage (NAS) or a storage area network (SAN). DAS might be cheaper, but NAS and SAN can usually better support large-scale operations, with SAN offering more availability and reliability.
Hyper-converged infrastructure (HCI) uses DAS to provide pooled storage resources, which has proved to be an effective strategy for VDI workloads. IT teams should evaluate each option to understand how it affects their circumstances.
Storage interfaces and protocols can also affect VDI performance. Common interfaces include Serial Advanced Technology Attachment (SATA), Serial Attached SCSI, Fibre Channel and Peripheral Component Interconnect Express. Common protocols include the Small Computer System Interface (SCSI), Internet SCSI, Advanced Host Controller Interface (AHCI), non-volatile memory express (NVMe) and non-volatile memory express over fabrics (NVMe-oF).
When IT combines the interface with the optimal protocol, it can make a significant difference in throughput and performance. The network fabric that supports communications, such as Ethernet or InfiniBand, can also affect throughput and performance. For example, Fibre Channel interfaces perform better than SATA interfaces, and the NVMe protocol is faster than AHCI.
The technologies around interfaces, protocols and network fabrics are changing rapidly, and IT teams must carefully evaluate the available options before making a choice.