I want to share some thought around our recent IBM SDI reference architecture work which I had the privilege to lead architecturally from our side. When we initiated our work last year, identifying the most suitable desktop virtualization solutions to be included was a critical starting point.

IBM and Citrix clearly enjoy a long and successful relationship, but, importantly, my personal experience in working with clients over the last few years has underlined the increasing interest in Citrix technologies, especially for larger-scale desktop virtualization deployments.

The Citrix FlexCast delivery technology in XenDesktop® resonates well with our customers, with its broad use case coverage and a “one desktop does NOT fit all” philosophy. IBM understands well that there are multiple approaches to desktop and application virtualization and the ability to architecturally match any type of virtual desktop or application to the appropriate delivery technology is appreciated by architects like me and consumers alike.

Why XenDesktop? In the area of hosted virtual desktops, the most commonly cited reasons by our customers for selecting XenDesktop stretch from its multi-hypervisor integration capability to the leading-edge Citrix HDXtechnology. This, combined with the extended capabilities provided by the Citrix NetScaler® product family and the company’s rich heritage in the end-user computing space made Citrix XenDesktop an obvious choice for our reference architecture.

So what have we been doing?

In the spirit of “customer choice is king”, we’ve set up three virtual desktop solutions in IBM labs in the U.S. and the UK and performed architecture verification and LoginVSI performance tests on different sets of IBM hardware, including IBM Blades and IBM Rack systems. We also tested the recently announced IBM PureSystems, an integrated system that combines compute, storage, networking, virtualization and management into a single infrastructure system and has therefore great potential to become the ideal platform for virtual desktop deployments.

IBM SmartCloud Desktop Infrastructure Figure 1 – IBM SmartCloud Desktop Infrastructure

The key design principle of our Reference Architecture is to address the arguably most common practical inhibitor to VDI – storage cost. Our approach allows the radical reduction of shared storage requirements for your VDI deployment by favouring local SSD storage instead of large-scale shared storage arrays for the performance intense write operations that occur in most VDI environments.

IBM SDI Reference Architecture Approach Figure 2 – IBM SDI Reference Architecture Approach

This approach is primarily based on a stateless or non-persistent relationship between the user and the virtual desktop image so that users can continue operations even in case of a host failure which renders the local storage inaccessible.

Citrix Provisioning Services (PVS) has inherently facilitated this concept, since its origin by creating and provisioning virtual desktops from a single desktop image (vDisk) on demand, optimizing storage utilization and providing a pristine virtual desktop to each user every time they log on. In addition to the described storage savings the use of a shared “master image” also allows for simplified image management.

Citrix Provisioning Services Figure 3 – Citrix Provisioning Services

It is important to point out that our reference architecture also facilitates dedicated desktop scenarios (or hybrids of stateless and dedicated).

A key objective for our architectural work was to determine the supported maximum user density for individual workloads in order to create scalable building blocks and sizing models – essentially make sure our approach works, scales and gets you to the best price point.

We tested PVS 6.1 delivered virtual desktops with the PVS write cache residing on local SSD storage (rather than shared storage) and measured all relevant performance metrics including disk IOPS, latency and network utilization. We determined VSImax – a benchmark number to describe maximum user density under acceptable response time – using a range of realistic workloads against the XenDesktop 5.6 environment.

The Intel X5690 based “Westmere” systems showed an impressive VSImax of 131 users but the equivalent workload tested on the new PureSystems achieved 174 users out of the box (without e.g. flash offload or other optimization) – an increase of over 30%!

VSImax XenDesktop HDX PureSystems Medium Workload+Flash Figure 4 – VSImax XenDesktop HDX PureSystems Medium Workload+Flash

We carefully monitored the IOPS rates and latency on the local disk subsystem generated by the PVS write cache activity to ensure that no bottlenecks were observed. Although IOPS rates clearly exceeded 1000 operations per second the latency never exceeded 3 milliseconds (up to 20 milliseconds are considered generally tolerable, so stayed well below that threshold)

IOPS measured on local SSD (PVS) Figure 5 – IOPS measured on local SSD (PVS)

We then worked closely with our Citrix counterparts to translate our insight into user density and performance metrics into scalable VDI building blocks based on IBM hardware (POC system, 300, 450, 1500 and 10 000 users).

IBM SmartCloud Desktop Services Figure 6 – IBM SmartCloud Desktop Services

With IBM’s ability to provide choice rather than a “one size fits all” approach, our leading-edge hardware platforms like IBM PureSystems and IBM’s longstanding expertise in providing implementation services using time-tested methodologies and tools developed through real-world client implementations we aim to be the “partner of choice” for desktop virtualization and look forward to a longstanding relationship with Citrix in this space!

Also check out Mike Ballengee’s blog here and Krishna Subramanian’s blog here.

More information on the partnership between Citrix and IBM, including collateral and scalability guides can be found at www.citrix.com/ibm and on IBM’s website at http://www-935.ibm.com/services/us/en/it-services/citrix.html

IBM servers that are certified with Citrix XenServer can be found at www.citrixready.com and at http://hcl.vmd.citrix.com/.

Andreas Groth
Lead Architect
IBM ATS Europe – x86 Virtualisation & Cloud