By Gus Chavira, Senior Solution Architect
VDI deployments can create high demands on your storage platforms. These demands manifest themselves in the form of various storage storm activities such as boot, logon/logoff, virus scan, and various user-initiated desktop operations. This can create a chaotic and unpredictable storage experience that is uniquely challenging in the VDI desktop space. We cannot simply build out storage requirements according to steady state activities (although that is the larger consideration) but need to ensure the storage systems have the capabilities to handle these unpredictable events. IOPS generated per desktop can vary greatly depending on the user type. For example, knowledge workers with several demanding applications can create significantly higher IOPS per desktop than task workers performing routine operations.
Segue to an introduction of The Dell Compellent SC8000 All Flash Array (SC8000 AFA) with its advanced storage architecture and feature set, combined with tight hypervisor integration, provides an automated, self-tuning storage system capable of efficiently scaling to satisfy production-level VDI workloads.
General lab testing info
While this exercise was completed in Dell labs with XenDesktop VDI brokered desktops on VMware vSphere hypervisor (same as what would be used in VMware Horizon View), the workload footprint is identical to VMware Horizon View and the predicable and tested results will be extremely close if not the same. Regardless of the type of VDI brokerage you are working with, the Compellent SC8000 AFA can meet your needs.
In recent lab testing, it was demonstrated that 3000 virtual desktops could be deployed while maintaining a good user experience. This was done using a very compact solution consisting of a single SC8000 AFA with a pair of controllers and one enclosure of 24 Solid State Drives (SSDs). A medium-heavy workload was used in order to generate numbers that were representative of a real-world implementation and not artificially inflated. This workload generated 30 IOPS per desktop at steady state. The SC8000 AFA performed very well against this workload, and did so at less than 3.5ms (goal was to be less than 10ms) of storage latency which made for an excellent end-user experience.
Hardware details for testing
- Dell PowerEdge M620 blade servers for VDI workload
- Dell PowerEdge M710HD blade servers for infrastructure hosting
- Dell PowerConnect 8024-k blade switches
- Dell Force10 S4810 Top of Rack (ToR) switch
- Brocade 5100 Fibre Channel (FC) ToR switches
- Dell Compellent SC8000 storage array running 6.4 Firmware
- All front end ports were 8 Gb FC and all back end ports were 6 Gb serial attached iSCSI (SAS)
- All SSD drives were 400 GB Single-level Cell (SLC) drives composed of 23 active drives + 1 hot spare
- Infrastructure storage was an SC8000 AFA running version 6.3 firmware. All front end ports were 8 Gb FC and all back and ports were 6 Gb SAS. The array used a combination of SSDs and spinning media. The role of the infrastructure storage is purely to provide storage for domain controllers, launchers, VDI brokerage servers, and other miscellaneous server roles.
Architectural overview diagram
Primary test objectives
The primary objectives of the tests conducted for this paper were:
- Understand the performance impact on the storage array during the peak VDI I/O activity such as boot and login storms
- Determine the latency at the full steady state user load of 30 IOPS per desktop
Testing
Testing was conducted using the normal Desktop Virtualization Solution Engineering and Cloud Client Computing testing methodologies which utilize the built-in Login VSI 4 workloads and desktop templates optimized for VDI. Various methods of controlling VM boot rate and login rates were employed to gather statistics to determine maximum capabilities. Login VSI’s normal workloads were not setup to generate more than around 7.5 IOPS per desktop, and as noted earlier, the test requirements were to generate something significantly higher in the 30 IOPS per desktop range. To supplement the IOPS and get the desktops into the range that the test required, IOmeter was employed. The additional IOPS created by IOmeter was approximately 22.5 IOPS. Combined with the 7.5 IOPS generated by Login VSI’s normal workload yielded a total of 30 IOPS per desktop.
Testing results
Boot Storm results – Hopefully, this is not a common occurrence in a production VDI deployment, but it can happen after a power failure, maintenance procedure, or a catastrophic occurrence where all the desktops have to boot at the same time. Various measures can be employed to minimize the effect such as a staggered system boot delay, fixed boot times based on local office time, etc. The SC8000 AFA performed optimally under these conditions.
Login Storm results – This situation most commonly occurs during the start of each business day. During this test there was a brief spike in latency at the end of the desktop’s login phase as the environment transitioned to a steady state. During this entire period, latency did not exceed 10 ms (spike rose to just 7.5 ms for a very brief amount of time). This is a good indication that the user experience did not suffer during the login phases. A maximum of 93,000 IOPS were achieved with a read/write ratio of 5% read and 95% writes.
Steady State results – This is a very important test because it represents the majority of time that the infrastructure (and storage) will be operating under in a healthy VDI deployment. This directly correlates to the most important perception of user experience from the end-users. If performance is good here the user will most likely have the perception of a good desktop. In this test cycle, the SC8000 AFA array with a pair of controllers, 24 SLC SSDs in a single SC220 enclosure delivered 90,000 IOPS with approximately 3.5ms of storage latency for 3000 VDI desktops at 30 IOPS each resulting in an excellent user experience.
Conclusion
For VDI environments with challenging or unpredictable bursts of data, higher-end workloads, or a large number of condensed users where a compact footprint for storage is required, the Compellent SC8000 AFA is the solution. This storage platform is more than adequate for demanding VDI environments, and with its compact footprint you can conserve rack space without compromising on performance.
For additional information including detailed testing results, please click here.