You don’t need to be a rocket scientist to see the value in RAM Cache

A few years ago, we replaced all of our windows in our home (I’m talking about the panes of glass you look through, not the operating system). We, of course, talked with a few different companies who stopped by, went through their product portfolio and brought along samples. One demonstration stuck with me. The sales person, placed his sample window flat on the ground and stood on it, demonstrating the strength of the window. I immediately started thinking, “That was totally wicked” and “I wonder if it has ever shattered before”.

As the practical part of my brain kicked in, I began to wonder when I am ever going to need to walk on my windows. Is Batman stopping by and going to climb up my house? Is this unique to this particular window? Not knowing much about windows, I wondered if my old windows were just as strong.

Demos are meant to impress us, but we need to ask ourselves if the demo really demonstrates everyday life.

And this was the goal I set out to achieve when I was trying to see how much of a benefit to the user experience would the new RAM Cache with Disk Overflow feature provide. I wanted a demonstration that showed a very typical user.

A typical office user, like myself, uses a Windows desktop with the following

  1. Outlook
  2. Internet Explorer
  3. Microsoft Word

Even with the apps defined, you can still have quite a difference in the workload depending on the websites you visit or the type of document you create. Instead of visiting a website going overboard with multimedia, was used as it resembles a simple, common site.

Instead of creating a large, document, multiple pictures, different aspect ratios and 3d rendering, the demo creates a small document with a single paragraph and a simple chart.

With this simple workload, would we see any noticeable difference in the user experience? And by noticeable, I’m not talking about an application take a 1/2 second longer to load. I’m talking about a “WOW, anyone who sees this will definitely be able to notice the improvement”.

In this very simple demonstration, with a minimal workload, I saw 2 major things

  1. A drastic drop in disk activity
  2. Very noticeable change in the user experience

Try it for yourself. Flip the switch

From the virtual mind of Virtual Feller

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ESG Lab Spotlight Report: Up to 80% Reduction in Storage Cost for VDI and RDS

You’ve heard the news, you’ve seen the videos, and now the storage savings have been verified! According to an ESG report, the new RAM Cache with Disk Overflow feature, included in the XenApp and XenDesktop 7.6 release, has the potential to reduce storage costs by 80% or more. Now before you stop reading thinking this is too good to be true, think about the storage cost problem for a moment.

Storage costs associated with RDS/VDI solutions is for throughput and not space. We need to have enough throughput or IOPS so the user experience doesn’t suffer. And believe me, it can suffer drastically, as you can easily see in this simple demonstration (pay particular attention from the 3 to 4 minute mark J).

To visualize how this works, take the following diagrams into perspective

IO is destined for the disk. Disks are slow when compared to RAM. So the Cache on RAM with Overflow feature substitutes RAM for disk. And because RAM is not infinite, we will overflow portions of the RAM to disk as needed. But even this overflow is more efficient. The overflow is sequenced and consolidated into large, sequential blocks of data instead of small, random blocks.

Many implementations required massive SANs or expensive SSDs. People were spending large amounts of money on storage, not for space, but instead to achieve the throughput required by RDS/VDI. With the Cache on RAM with Overflow feature, we can drastically reduce the number of disks. We don’t need hundreds of disks to give us our throughput. We don’t need to implement SSDs. We can drastically reduce our disk count and focus more on storage space, which is by far, easier and cheaper to implement.

According to the ESG report on Provisioning Services, when you focus on disk throughput

  • A XenDesktop implementation requiring 26 disks can be reduced to 3
  • A XenApp implementation requiring 74 disks can be reduced to just 4

And because of the way this feature works, it provides value to multiple hypervisors.

From the virtual mind of Virtual Feller

PROOF[Video] – New XenDesktop and XenApp Storage Optimizations Does Improve the User Experience

I’ve written and seen numerous blogs/tweets about how great the new storage optimization feature is for XenApp and XenDesktop. I’ve read how this feature can reduce IOPS from an average of 15 IOPS per Windows 7 user down to 0.1 IOPS. I’ve read how this feature functions by creating a small RAM buffer within each VM. I’ve seen tweets showing crazy IOPS numbers on using standard, spinning disks.

In fact, I’ve done some of this analysis and was completely blown away by the results.

But who cares? Who cares if my IOPS are reduced by 99%?

Unfortunately, unless you are responsible for storage, you probably don’t care.  But what if this drastic reduction in IOPS had a direct impact on the user experience?  And from someone who uses VDI remotely 100% of the time, the user experience is what I really care about.

Let’s see what the new RAM Cache with Disk Overflow feature can do for the user experience…

What impresses me the most is that the workload used isn’t some crazy operation that a typical user wouldn’t really do.  You can easily see the improvement to the user experience with something as simple as browsing a few web pages.

And all of this is done

  • Without complex configurations
  • Without expensive SANs
  • Without SSDs
  • Without additional hardware
  • Without additional licenses
  • Without a learning curve

From the virtual mind of Virtual Feller

Upgrading from XenApp 7.5 to XenApp 7.6

After delivering the XenApp 7.6 Upgrade webinar, I received a few questions asking if it is a good idea to upgrade from XenApp 7.5 to XenApp 7.6. My first reaction is, “Of course you should. Why wouldn’t you?”

But I’m a little biased J

You need to ask yourself if the new features within XenApp 7.6 are important enough to upgrade. Look at the following subset of features and determine if they are something that would be valuable for your users and admin:

  1. Unauthenticated Logons: This feature allows a user to access an application without being required to authenticate. This feature is mostly used in healthcare. If you need this, you must go to XenApp 7.6 feature
  2. Connection Leasing: You ever watch Star Trek and you hear the engineers talk about having secondary backups? A secondary backup won’t let your starship reach Warp 9, but it will keep your ship from exploding. That is essentially what connection leasing does for your XenApp site. Your first layer of backup is configuring your database to be highly available (mirroring, clustering or AlwaysOn). If that fails, you want to have a secondary backup, which is connection leasing. Another XenApp 7.6-only feature
  3. App Usage: Provides additional reporting capabilities for admins so they can see usage patterns for the applications. It’s good to know what your users are using.
  4. Fast App Access: “Patience you must have, my young padawan” is great if you are a Jedi. Unfortunately, my patience decreases waiting for my logon. A Windows logon includes a list of things (policies, logon scripts, drive mappings, etc.) that must execute before you can get to an application. Fast App Access essentially does all of the session creation processes before you request an app, greatly reducing logon times. In a production environment, the logon process that the user experiences is as follows:

    Take a look at the Session Prelaunch video to see how it is configured and functions.

What’s nice about being on XenApp 7.5 and upgrading to XenApp 7.6 is that the upgrade path is very easy. At a high-level, you essentially do the following:

You will notice that these are all upgrades. No need to rebuild. Of course, if you want more detail and guidance, then take a look at the following eDocs article.

The XenApp 7.5 to 7.6 upgrade is probably one of the smoothest upgrades I’ve ever done, and I’ve been upgrading since WinFrame.


From the virtual mind of Virtual Feller

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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