Diving deeper into the latest XenDesktop 7.5 IOPS results

As you saw in a previous blog, XenDesktop 7.5 is able to achieve an average IOPS value of less than 1/10th per user. Of course when you put out unbelievable results like this you hear a lot of comments trying to find holes in the results or test procedures. This is as it should be as it is part of any good scientific method.

In order to show a more complete picture of the value of the new Provisioning Services Ram Cache with Disk Overflow, we gathered additional details from the Citrix Solutions Lab’s tests. This set of data includes details for the duration of the entire test that included logons for roughly 100 users (sorry but it didn’t include boot. However, booting is mostly a read operation that PVS can handle with server-side cache).

The results are still just as stunning as the steady state:

For a physical host, we accumulated IOPS numbers for each of the virtual desktop sessions then combined into a single graph. As you can see, during the logon portion of the test we had a peak, and I mean maximum IOPS value, of 12 IOPS.

What if we don’t break it down by user, what would the host’s total IOPS graph look like?












The absolute peak is 155 IOPS on a host that is running 100 VDI VMs.

Tests details were as follows:

  • LoginVSI 4.0 medium workload
  • Hypervisor: Hyper-V 2012R2 and vSphere 5.5
  • Virtual Machine: Windows 7, 2 vCPU and 2.5 GB of RAM (512 MB as defined for the RAM Cache)

Based on results like this, I’m left to wonder how many users I can support on my mid-1990s college PC (Pentium 486 with a 420MB hard drive) J

From the virtual mind of Virtual Feller

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Latest XenDesktop 7.5 IOPS

It is amazing when you’ve been focused on a technology for so long that you start to see major improvements. In 2010, I provided my original guidance on XenDesktop IOPS. Four years later, have we seen any major improvement? See for yourself.

As you might be aware, I’ve been working with the Citrix Solutions Lab on validating standardized designs. These validated designs are published as Citrix Design Guides. Part of this latest round of testing with XenDesktop 7.5 and XenApp 7.5 was focused on the new Provisioning Services write cache option “RAM Cache with Overflow to Disk”. When looking at XenApp 7.5, we observed some astounding results, as detailed in the following blogs:

In addition to these, Dan Allen also released a blog on “Turbo-Charging Your IOPS – Part 2” that showed additional impressive results.

But back to the Solutions Lab testing… I’ve finally started going through the results from the XenDesktop 7.5 portion of the test. And what we see is even more amazing than the XenApp tests (which were impressive).

Using the medium workload from LoginVSI 4.0, we observed the steady state IOPS following:

  • MCS: 10 IOPS
  • PVS with Disk Cache: 9.2 IOPS
  • PVS (RAM Cache with Overflow to Disk): 0.09 IOPS

And before you ask, we saw very similar results with vSphere 5.5

We used Windows 7 virtual machines with 2 vCPU and 2.5 GB of RAM (512MB was defined for the RAM cache)

With this one feature within Provisioning Services, we got steady state IOPS to be less than 1/10th of an IOPS without any special configurations. Impressive

The main challenge I see is how the Provisioning Services team will improve upon this. All I can say is “Good luck!”

From the virtual mind of Virtual Feller

The Latest XenApp 7.5 Read/Write Ratios

As technology changes, so too does a recommendation.

For years when you deployed XenApp servers with Provisioning Services, the storage Read:Write ratio would be 10:90. This is still the case in most scenarios. But in analyzing the latest data from the Citrix Solutions Lab, who were testing the “RAM Cache with Overflow to Disk” option, we encountered some results that will make us revisit some of our old recommendations.

  1. IOPS: For a medium workload on XenApp 7.5 on Hyper-V 2012R2, the average IOPS per user is 1, as explained in the previous blog.
  2. R:W Ratio: When using the new write cache option on Hyper-V 2012R2, the read:write ratio changes to 40:60. (Note: These numbers are taken at the physical host layer and not the VM layer)

Why is this? Why the change?

Think about what the RAM Cache with Disk Overflow does… It uses a section of allocated VM RAM to cache disk activity. As this cache fills up, it will start to move portions to disk. If you allocated enough RAM, you significantly reduce the number of IOPS (especially write IOPS). Look at the differences between PVS Disk and RAM Cache options

We’ve significantly reduced write activity because writes go to RAM. And whatever writes do make it to disk from the RAM Cache are bigger block sizes, thus also helping to reduce IOPS.

And finally, if you look at the disk idle time on the physical host, you can clearly see that the disks have a higher idle percentage when using the new RAM Cache with Disk Overflow option within PVS because we have less data going to the disk.

So far, the RAM Cache with Disk Overflow option is looking very promising. Soon, I’ll show you what it can do for Windows 7 workloads

For this setup, we used

  • LoginVSI 4.0 with a medium workload
  • Hyper-V 2012R2
  • XenApp 7.5 running on Windows Server 2012R2
  • 6 vCPU, 16GB RAM, 2 GB RAM Cache
  • 7 VMs per physical host

From the virtual mind of Virtual Feller

Latest updates to the Citrix Visio Stencils

As you saw in a previous blog, I created a new set of Visio stencils for XenApp 7.5 and XenDesktop 7.5 that included full diagrams within the stencil (I’m still impressed with this idea J)

Over the last few months, I’ve had to create a few more architecture diagrams and realized I needed a few more items. I’ve incorporated them into the latest stencil update. Recent additions include:

  • New virtual desktop model: DesktopPlayer
  • New user roles: User, Admin and Support
  • New hardware: SSD and HDD

Links to the latest stencils are:

From the virtual mind of Virtual Feller

The Choice is yours in the Citrix Cloud

Synergy 2014 is over and while I work to catch up with everything else (apparently life does move forward outside of Synergy), I keep thinking about one keynote demo that really made me stop and think… Citrix Workspace Services.

Based on my understanding, you can think of Citrix Workspace Services as the following (these are the brief notes I took during the keynote):

  1. Citrix provides a “Control Plane” running in the cloud (It happens to be on Azure if you are wondering)
  2. The Control Plane lets an organization spin up a XenApp or XenDesktop environments anywhere

This is a pretty easy concept at the high-level, but the more I think about this, the more interesting it becomes.

Every solution must include

  • Physical layer resources (the hardware) – The physical layer resources can be anywhere. They can be in any number of IaaS providers (Azure, AWS, CloudPlatforms, etc., etc., etc.), or they can be within your own data center.
  • Control layer resources (the management). The control layer resources must be accessible from anywhere so that administrators can support their environment even when they are travelling and out of office and the control layer resources must be able to access the physical layer components located anywhere.

Now here is what gets me really excited about this idea… (Remember, this was just a keynote demo. I’m not sure what functionality it will have, how it will work, or how all of the nuts/bolts fit together. This is all my speculation).

  • The cloud frightens me: Many of the concerns with a cloud-hosting is that they are risky and that there is a risk that the IaaS vendors can see your data and know all of your secrets. Every organization has secrets and they don’t want them in the cloud but every organization also has other resources that can be in the cloud. (Do you think KFC will put the Colonel’s secret chicken recipe in the cloud?). With Citrix Workspace Servers every organization can have a single solution where portions of it are within the on-prem data center while other portions are in the cloud.
  • IaaS Does Not Own Me: One of the biggest concerns I hear when people think about moving to the cloud is that they are locked into to the provider (much worse than trying to cancel your fitness club membership). It sounds like Citrix Workspace Services might make this easy to overcome. Let’s say you deliver your apps from AWS and next year you find that you will get better results with Azure. You don’t have to re-design your entire solution or learn a whole new solution. All you will need to do is go into Citrix Workspace Services and deploy a new solution on Azure while you shut down your AWS deployment. What about migrating machines/data? No idea yet as this as still just a demo.
  • I want to deliver something good too: Let’s say I’m a service provider and want to get into the hosting game. This would appear to make my life easier. I don’t need to setup my own infrastructure, I can leverage Citrix Workspace Services and let it build my environment on any platform I choose. I can then build my own services around it.

Seems like Citrix Workspace Services brings a whole new meaning to any, any, any.

Virtual Feller’s virtual thoughts


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