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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

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

One Imaging Solution to Rule Them All

As we all know, a single image management solution is extremely important in the VDI world. We will have hundreds or thousands of desktops that must be built and maintained. Image management is even more important when we have stateless desktops because we want our desktop to be reset to its original state after each user session. If you are doing stateless desktops without some form of image management in order to keep the desktops identical on initial startup, people would think you are crazy (and I think you would be).

What about RDS-based (session virtualization) implementations? I don’t hear much discussion on the need for image management with session virtualization. Is it because it is simply a common sense requirement that everyone already does or is it because people believe that you can get by without it?

Just in case it’s the latter, that’s take a trip in the “Wayback machine” (sorry, just saw Mr. Peabody and Sherman with my kids) to the 1990s and remember the world of WinFrame and MetaFrame and a world without single image management. We would build MetaFrame servers with Ghost, automated scripts and other deployment tools. They worked great. They let us build servers without having to sit in front of a screen all day hitting Next, Next, Next and did I mention Next. Deployment was easy. And then, a week or two later, you would start to hear the user complaints…

My app worked correctly yesterday, but it doesn’t today

Why is this different than it was yesterday?

Where did my add-on go?

This sucks. I hate it.

It all came down to a single reason, although our servers were built identically, they start to take on a unique persona once the server is turned on. And when users start connecting and doing things (work), the servers change more and more. Eventually, you begin to hear the users and life is no longer good if you are the IT Admin.

This was a major issue for every organization, which is why we have Provisioning Services. Regardless if your server is physical or virtual, they will be identical because Provisioning Services delivers a single image to every target. And Provisioning Services makes sure those targets remain consistent because on startup, each target starts at a clean state.

There are also some organizations that will want to extend their session virtualization environment to include VDI desktops. It only makes sense that your enterprise image management solution should be able to handle physical and virtual VDI, physical and virtual RDS and any other combination.

Before single image management solutions like Provisioning Services and Machine Creation Services came around, a user’s computing workspace was like a box of chocolates, you never knew what you were going to get.

Virtual Feller’s virtual thoughts

True or False: Citrix Provisioning Services requires PXE

Test your Citrix knowledge…

True or False: Citrix Provisioning Services requires PXE

Answer: False

When using Provisioning Services, which is an optional component of XenDesktop, the target device utilizes a bootstrap file, which initializes the Provisioning Services stream. The target device must be able to obtain that bootstrap file, or else the stream will never begin.

Unfortunately, I still hear people saying that the only way to accomplish this is with PXE, which is incorrect.

Provisioning Services has a few different options for delivering the bootstrap file (these have been the most common approaches for many years):

  1. The DHCP Method:
    Target device boots and sends DHCP discover broadcast
    DHCP server responds with a client IP, Option 66 & 67
    Target device uses the IP and contacts the server identified in Option 66 requesting the file from option 67.
    The PVS server sends the requests bootstrap file via TFTP to the target device.
  2. The PXE Method:
    Target device boots and sends DHCP discover broadcast with Option 60 PXE Client
    DHCP server responds with IP
    PVS Servers, which are running PXE Services, respond with Boot Server
    Client uses the IP and picks one of the PVS responses and requests more information
    PVS responds with boot server/file name information
    Target device contacts the boot server and requests the file name.
    The PVS server sends the requests bootstrap file via TFTP to the target device.
  3. The Local Method: An local file is created with the Boot Device Manager, a component of Provisioning Services. The local file is the bootstrap file, which tells the target how to contact the Provisioning Services farm. It is assigned to each target device either as an ISO attached to the target deices DVD drive, a USB drive, or as a small attached virtual hard disk drive.

It is a pretty good mix of organizations opting for DHCP or Local, much less using the PXE method. Both work, but DHCP and PXE requires more integration with your current environment than the Local method.

Daniel – Lead Architect


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