Guest Post by Anjan Srinivas, Director of Product Marketing, Atlantis Computing
Correct IO sizing can be a challenge for customers adopting VDI. Storage can represent between 20 and 70% of the total desktop cost in VDI infrastructure. Get it right and the project is successful – users accept it and desktop cost is low. Get it wrong and the desktop costs can rise, and the team may not get to scale beyond the first implementation – or the desktop is inexpensive and users reject it for performance reasons.
The Windows OS was designed with a local and dedicated disk and requires constant access to the hard drive even when it is idle. In addition, the Windows OS will consume as much disk IO or throughput to the hard drive as is available. Windows desktop workloads are write heavy (70-80% writes, 20-30% reads) .Windows 7 OS images are also larger than XP images, forcing enterprises to buy more storage capacity to accommodate larger numbers of users( a Windows 7 image ranges from 25GB to 50GB or more depending on the components and apps installed).
There is another problem with IOPS when it comes to VDI. All IOPS coming out of virtual desktops are typically treated as “equal” by the hypervisor. This causes a lack of consistent user experience (as user workloads vary). Imagine a user running a zip file compression or running an on-demand virus scan on the same host as the CEO who needs his desktop to work on his board meeting presentation.
So why is IOPS a limiting factor?
Essentially the problem comes down to the physics of a spinning disk. In a traditional hard disk drive there is a spinning platter which is why all disks have an RPM value. Each disk can provide 65-150 IOPS per spindle depending on what type of disk is being used in the array. Customers sometimes size for the storage capacity or average IOPS. Both these approaches may result in under sizing the storage resulting in poor user experience. When sized for peak IOPS, the number of disks make the solution very expensive and raises the cost per user. It should be noted, that as of View 4.6, the concept of tiered storage was introduced…that is the ability break up the VDI workload and place different components on different types of storage. The impact is that it is now possible to put the linked clone image on SSD on the compute host, which offers a high performance experience for users (fast app launch times) as well as an improved IT experience.
What Else is Possible?
Even with the tiered storage support in View, there is also another approach customers can take to overcome IO challenges using a storage optimization solution. ILIO is NTFS aware and with its advanced IO processing and inline de-duplication it offloads the IOPS before it reaches storage. This results in lower storage capacity consumed and high performing desktop because write and read IO offload provided by ILIO. Being software, Atlantis ILIO is storage and hardware agnostic- customers no longer need to worry about qualifying new hardware vendors and buying new hardware and can leverage what they have. ILIO solution is optimized for both XP and Win7 images and supports both stateless and persistent desktops. Atlantis ILIO works in conjunction with advanced vSphere features like vMotion / DRS / HA and FT.
So what does performance look like with ILIO? Well you can expect to support high performance desktops (300+ IOPS per desktop) with up to 90% less cost when it comes to storage. You can actually support 4 to 7x more users on your existing infrastructure – SAN, NAS, local disk or even diskless (memory) options.Find out more about the IO offload and capacity improvements for a high performance desktop (300 IOPS – 2x you the PC performance) VMware View 5 desktop in the reference architecture published here. This RA includes View 5, VMware ThinApp, View Persona and View Planner tools.
Offloading Virtual Desktop IOs with Atlantis ILIO: Deep Dive – By Andre Leibovici
View Calculator with Atlantis ILIO – By Andre Leibovici