To understand what I mean, let’s think for a moment about what a “hypervisor” is in the server virtualization world. Whether you’re talking about VSphere, Hyper-V, or XenServer, you’re talking about software that provides an abstraction layer between hardware resources and operating system instances. An individual VM doesn’t know – or care – whether it’s running on an HP Server, a Dell, an IBM, or a “white box.” It doesn’t care whether it’s running on an Intel or an AMD processor. You can move a VM from one host to another without worrying about changes in the underlying hardware, bios, drivers, etc. (Not talking about “live motion” – that’s a little different.) The hypervisor presents the VM with a consistent execution platform that hides the underlying complexity of the hardware.

So, back to DataCore. Remember that SANsymphony-V is a software application that runs on top of Windows Server 2008 R2. In most cases, people buy a couple of servers that contain a bunch of local storage, install 2008 R2 on them, install SANsymphony-V on them, and turn that bunch of local storage into full-featured iSCSI SAN nodes. (We typically run them in pairs so that we can do synchronous mirroring of the data across the two nodes, such that if one node completely fails, the data is still accessible.) But that’s not all we can do.

Because it’s running on a 2008 R2 platform, it can aggregate and present any kind of storage the underlying Server OS can access at the block level. Got a fibre channel SAN that you want to throw into the mix? Great! Put fiber channel Host Bus Adapters (HBAs) in your DataCore nodes, present that storage to the servers that SANsymphony-V is running on, and now you can manage the fibre channel storage right along with the local storage in your DataCore nodes. Got some other iSCSI SAN that you’d like to leverage? No problem. Just make sure you’ve got a couple of extra NICs in the DataCore nodes (or install iSCSI HBAs if you want even better performance), present that iSCSI storage to the DataCore nodes, and you can manage it as well. You can even create a storage pool that crosses resource boundaries! And now, with the new auto-tiering functionality of SANsymphony-V v8.1, you can let DataCore automatically migrate the most frequently accessed data to the highest-performing storage subsystems.

Or how about this: You just bought a brand new storage system from Vendor A to replace the system from Vendor B that you’ve been using for the past few years. You’d really like to move Vendor B’s system to your disaster-recovery site, but Vendor A’s product doesn’t know how to replicate data to Vendor B’s product. If you front-end both vendors’ products with DataCore nodes, the DataCore nodes can handle the asynchronous replication to your DR site. Alternately, maybe you bought Vendor A’s system because it offered higher performance than Vendor B’s system. Instead of using Vendor B’s product for DR, you can present both systems to SANsymphony-V and leverage its auto-tiering feature to automatically insure that the data that needs the highest performance gets migrated to Vendor A’s platform.

So, on the back end, you can have disparate SAN products (iSCSI, fibre channel, or both) and local storage (including “JBOD” expansion shelves), and a mixture of SSD, SAS, and SATA drives. The SANsymphony-V software masks all of that complexity, and presents a consistent resource – in the form of iSCSI virtual volumes – to the systems that need to consume storage, e.g., physical or virtual servers.

That really is analogous to what a traditional hypervisor does in the server virtualization world. So it is not unreasonable at all to call SANsymphony-V a “storage hypervisor.” In fact, it’s pretty darned clever positioning, and I take my hat off to the person who crafted the campaign.

Maybe it is better than the other guy’s. But you might want to look closely at what was tested, how it was tested, and whether they were, shall we say, selective in the facts they present.

Case in point: The Tolly Group’s report, released May 27, comparing VMware View 4.6 Premier Edition to Citrix XenDesktop 5 Platinum edition. There are several interesting aspects to this report, which are dealt with in detail in Tal Klein’s blog over on the Citrix Community blog site. Here are a few of the more egregious items:

• VMware View 4.6 Premier licensing costs less than XenDesktop 5 Platinum. Absolutely true, and absolutely irrelevant. That’s like pointing out that if you load every possible dealer option onto your new car, it’s going to cost more than the basic model. Thank you, Captain Obvious. If you want an "apples-to-apples" comparison, you need to compare VMware View to the XenDesktop VDI Edition. But wait, if you do that, XenDesktop is actually less expensive, and that would be an awkward point to publish in a paper that’s being paid for by VMware.
• VMware’s PCoIP provides a more consistent multi-media experience than XenDesktop 5. (Over a LAN. Using a single thin client device that did not support any of the Citrix HDX media acceleration features.) Sorry, guys, but once again this is not an apples-to-apples comparison. And did they publish any results of testing across a WAN link? Nope…and for the same reason they didn’t use XenDesktop VDI Edition for their price comparison.
• It’s easier to upgrade View 4.5 to View 4.6 than it is to upgrade XenDesktop 4 to XenDesktop 5. Once again, both true and irrelevant. It’s easier to give your kitchen a new coat of paint than it is to rip out the cabinets and completely remodel it. Anybody surprised by that? There are significant architectural changes from XenDesktop 4 to XenDesktop 5. It shouldn’t be surprising to anyone that this will involve more effort than a "dot release" upgrade.

I’ve always been skeptical of vendor-sponsored "analysis" reports, and, to be fair, Citrix has used the Tolly Group in the past for its own sponsored reports – but it seems to me that this one is just over the top. Apparently, former Gartner analyst Simon Bramfitt agrees. His pithy assessment of the report: "There are undiscovered tribes lost in the darkest parts of the Amazon jungle that would know exactly what to do if a vendor airdropped a pile of competitive marketing literature authored by the Tolly Group; send it back, and asked [sic] that it be re-printed on more absorbent paper."

What do you think?

Just before writing this post, I went to the Dell Web site and priced out a low-end Vostro Mini Tower system: 3.2 GHz Intel E5800 dual-core processor, 3 Gb RAM, 320 Gb disk drive, integrated Intel graphics, Windows 7 Professional 64-bit OS, 1 year next-business-day on-site service. Total price: $349.00.

When you buy a new PC with an OEM license of Windows on it, you have 90 days to add Microsoft Software Assurance to that PC. That will cost you $109.00 for two years of coverage. You’re now out of pocket $458.00. However, one of the benefits of Software Assurance is that you don’t need any other Microsoft license component to access a virtual desktop OS. You also have the rights, under SA, to install Windows Thin PC (WinTPC) on the system, which strips out a lot of non-essential stuff and allows you to administratively lock it down – think of WinTPC as Microsoft’s own tool kit for turning a PC into a thin client device.

Now consider the thin client option. A new Wyse Winterm built on Embedded Windows 7 carries an MSRP of $499. There are less expensive thin clients, but this one would be the closest to a Windows 7 PC in terms of the user experience (media redirection to a local Windows Media Player, Windows 7 user interface, etc.). However, having bought the thin client, you must now purchase a Microsoft Virtual Desktop Access (VDA) license to legally access your VDI environment. The VDA license is only available through the Open Value Subscription model, and will cost you $100/year forever. So your total cost over two years is $699 for the Wyse device vs. $458 for the Dell Vostro.

After the initial two year term, you’ll have to renew Software Assurance on the PC for another two years. That will continue to cost you roughly $54.50/year vs. $100/year to keep paying for that VDA license.

Arguably, the Wyse thin client is a better choice for some use cases. It will work better in a hostile environment – like a factory floor – because it has no fan to pull dust and debris into the case. In fact, it has no moving parts at all, and will likely last longer as a result…although PC hardware is pretty darned reliable these days, and at that price point, the low-end PC becomes every bit as disposable as a thin client device.

So, as much as we love our friends at Wyse, the bottom line is…well, it’s the bottom line. And if you’re looking at a significant VDI deployment, it might be worth running the numbers both ways before you decide for sure which way you’re going to go.

In a nutshell, the problem is that a Windows desktop OS uses disk far differently than a Windows server OS. Thanks to the way Windows uses the swap file, disk writes outnumber disk reads by about 2 to 1. You can build your virtual desktop infrastructure on the latest and greatest server hardware, with tons of processing power and insanely huge amounts of RAM, but if all of the disk I/O for all of those virtual desktops is hitting your SAN, you’ve got a scalability problem on your hands.

Provisioning Services (“PVS”) can help to mitigate this in two ways (assuming for sake of argument that you’re provisioning multiple virtual systems from a common, read-only image): First, if you build your Provisioning Servers correctly, you should be able to serve up most of the OS read operations from the Provisioning Server’s own cache memory. Second, you can use the virtualization host’s local disk storage as the required “write cache” – because all of those write operations have to go somewhere while the virtual system is running.

But XenDesktop 5 introduced a new way to provision desktops called “Machine Creation Services” (“MCS”). We wrote about this in the April edition of our Moose Views newsletter, so if you’re not familiar with all the pros and cons of MCS vs. PVS, I’d encourage you to take a brief time out and read that article. Suffice it to say that, despite all the advantages of MCS, the biggest downside of using MCS to provision pooled desktops was that all of the IOPS hit your SAN storage, which limited the scalability of an MCS-provisioned VDI deployment.

But all of that just changed, with the release of XenDesktop 5 Service Pack 1, which was made available for download a week ago (May 13). With SP1, XenDesktop 5 is now able to take advantage of the “IntelliCache” feature that was introduced as part of XenServer v5.6 Service Pack 2. Using MCS with the combination of XenDesktop 5 SP1 and XenServer SP2…

• The first time a virtual desktop is booted on a given XenServer, the boot image is cached on that XenServer’s local storage.
• Subsequent virtual desktops booted on that same XenServer will boot and run from that locally cached image.
• You can use the XenServer’s local storage for the write cache as well.

The bottom line is that you can move as much as 90% of the IOPS off of the SAN and onto local XenServer storage, removing nearly all of the scalability limitations from an MCS-provisioned environment.

With most of the IOPS for running VMs taking place on local storage, it’s pretty straightforward to figure out how many VMs you can expect to support on a given virtualization host. Dan Feller’s blog post does a great job of walking through the process of calculating the functional IOPS that your local XenServer storage repository should be able to support, and inferring from that number how many light, normal, or power users you should be able to support as a result.

This also means that using XenServer as the hypervisor for your XenDesktop 5 deployment is going to yield a significant performance advantage over any other hypervisor, unless or until the other guys come out with similar local caching features. So, if you’re a VMware shop, my advice is this: Go ahead and virtualize all of the supporting XenDesktop server components on your VSphere infrastructure. Run your XenDesktop 5 VMs on XenServer hosts, and just don’t tell anyone! If you’re asked, just say, “Oh, yeah, these are my XenDesktop host systems – they’re completely separate from our VSphere infrastructure, because we don’t need the (insert favorite VSphere feature) function for these systems.” Your infrastructure will run better, and no one will know but you…

I have no doubt that the forensic analysis of what happened and why will drag on for a long time. Justin Santa Barbara had an interesting blog post last Thursday (April 21) that discussed how the design of Amazon Web Services (AWS), and its segmentation into Regions and Availability Zones, is supposed to protect you against precisely the kind of failure that occurred last week…except that it didn’t.

Phil Wainewright has an interesting post over at ZDnet.com on the “Seven lessons to learn from Amazon’s outage.” The first two points he makes are particularly important: First, “Read your cloud provider’s SLA very carefully” – because it appears that, despite the considerable pain some of Amazon’s customers were feeling, the SLA was not breached, legally speaking. Second, “Don’t take your provider’s assurances for granted” – for reasons that should be obvious.

Wainewright’s final point, though, may be the most disturbing, because it focuses on Amazon’s “lack of transparency.” He quotes BigDoor CEO Keith Smith as saying, “If Amazon had been more forthcoming with what they are experiencing, we would have been able to restore our systems sooner.” This was echoed in Santa Barbara’s blog post where, in discussing customers’ options for failing over to a different cloud, he observes, “Perhaps they would have started that process had AWS communicated at the start that it would have been such a big outage, but AWS communication is – frankly – abysmal other than their PR.” The transparency issue was also echoed by Andrew Hickey in an article posted April 26 on CRN.com.

CRN also wrote about “lessons learned,” although they came up with 10 of them. Their first point is that “Cloud outages are going to happen…and if you can’t stand the outage, get out of the cloud.” They go on to talk about not putting “Blind Trust” in the cloud, and to point out that management and maintenance are still required – “it’s not a ‘set it and forget it’ environment.”

And it’s not like this is the first time people have been affected by a failure in the cloud:

• Amazon had a significant outage of their S3 online storage service back in July, 2008. Their northern Virginia data center was affected by a lightning strike in July of 2009, and another power issue affected “some instances in its US-EAST-1 availability zone” in December of 2009.
• Gmail experienced a system-wide outage for a period of time in August, 2008, then was down again for over 1 ½ hours in September, 2009.
• The Microsoft/Danger outage in October, 2009, caused a lot of T-Mobile customers to lose personal information that was stored on their Sidekick devices, including contacts, calendar entries, to-do lists, and photos.
• In January, 2010, failure of a UPS took several hundred servers offline for hours at a Rackspace data center in London. (Rackspace also had a couple of service-affecting failures in their Dallas area data center in 2009.)
• Salesforce.com users have suffered repeatedly from service outages over the last several years.

This takes me back to a comment made by one of our former customers, who was the CIO of a local insurance company, and who later joined our engineering team for a while. Speaking of the ASPs of a decade ago, he stated, “I wouldn’t trust my critical data to any of them – because I don’t believe that any of them care as much about my data as I do. And until they can convince me that they do, and show me the processes and procedures they have in place to protect it, they’re not getting my data!”

Don’t get me wrong – the “Cloud” (however you choose to define it…and that’s part of the problem) has its place. Cloud services are becoming more affordable, and more reliable. But, as one solution provider quoted in the CRN “lessons learned” article put it, “Just because I can move it into the cloud, that doesn’t mean I can ignore it. It still needs to be managed. It still needs to be maintained.” Never forget that it’s your data, and no one cares about it as much as you do, no matter what they tell you. Forrester analyst Rachel Dines may have said it best in her blog entry from last week: “ASSUME NOTHING. Your cloud provider isn’t in charge of your disaster recovery plan, YOU ARE!” (She also lists several really good questions you should ask your cloud provider.)

Cloud technologies can solve specific problems for you, and can provide some additional, and valuable, tools for your IT toolbox. But you dare not assume that all of your problems will automagically disappear just because you put all your stuff in the cloud. It’s still your stuff, and ultimately your responsibility.

We’ve been playing with SANsymphony-V in our engineering lab, and our technical team is impressed with both the functionality and the new user interface – but that’s another post for another day. This post is focused on the packaging and pricing of SANsymphony-V, which in many cases can come in significantly below the old SANmelody pricing.

First, we need to recap the old SANmelody pricing model. SANmelody nodes were priced according to the maximum amount of raw capacity that node could manage. The full-featured HA/DR product could be licensed for 0.5 Tb, 1 Tb, 2 Tb, 3 Tb, 4 Tb, 8 Tb, 16 Tb, or 32 Tb. So, for example, if you wanted 4 Tb of mirrored storage (two 4 Tb nodes in an HA pair), you would purchase two 4 Tb licenses. At MSRP, including 1 year of software maintenance, this would have cost you a total of $17,496. But what if you had another 2 Tb of archival data that you wanted available, but didn’t necessarily need it mirrored between your two nodes? Then you would want 4 Tb in one node, and 6 Tb in the other node. However, since there was no 6 Tb license, you’d have to buy an 8 Tb license. Now your total cost is up to $21,246.

SANsymphony-V introduced the concept of separate node licenses and capacity licenses. The node license is based on the maximum amount of raw storage that can exist in the storage pool to which that node belongs. The increments are:

• “VL1″ – Up to 5 Tb – includes 1 Tb of capacity per node (more on this in a moment)
• “VL2″ – Up to 16 Tb – includes 2 Tb of capacity per node
• “VL3″ – Up to 100 Tb – includes 8 Tb of capacity per node
• “VL4″ – Up to 256 Tb – includes 40 Tb of capacity per node
• “VL5″ – More than 256 Tb – includes 120 Tb of capacity per node

In my example above, with 4 Tb of mirrored storage and 2 Tb of non-mirrored storage, there is a total of 10 Tb of storage in the storage pool: (4 x 2) + 2 = 10. Therefore, each node needs a “VL2″ node license, since the total storage in the pool is more than 5 Tb but less than 16 Tb. We also need a total of 10 Tb of capacity licensing. We’ve already got 4 Tb, since 2 Tb of capacity were included with each node license. So we need to buy an additional six 1 Tb capacity licenses. At MSRP, this would cost a total of $14,850 – substantially less than the old SANmelody price.

The cool thing is, once we have our two VL2 nodes and our 10 Tb of total capacity licensing, DataCore doesn’t care how that capacity is allocated between the nodes. We can have 5 Tb of mirrored storage, we can have 4 Tb in one node and 6 Tb in the other, we can have 3 Tb in one node and 7 Tb in the other. We can divide it up any way we want to.

If we now want to add asynchronous replication to a third SAN node that’s off-site (e.g., in our DR site), that SAN node is considered a separate “pool,” so its licensing would be based on how much capacity we need at our DR site. If we only cared about replicating 4 Tb to our DR site, then the DR node would only need a VL1 node license and a total of 4 Tb of capacity licensing (i.e., a VL1 license + three additional 1 Tb capacity licenses, since 1 Tb of capacity is included with the VL1 license).

At this point, no new SANmelody licenses are being sold – although, if you need to, you can still upgrade an existing SANmelody license to handle more storage. If you’re an existing SANmelody customer with current software maintenance, rest assured that you will be entitled to upgrade to SANsymphony-V as a benefit of your software maintenance coverage. However, there will not be a mechanism that allows for an easy in-place upgrade until sometime in Q3. In the meantime, an upgrade from SANmelody to SANsymphony-V would entail a complete rebuild from the ground up. (Which we would be delighted to do for you if you just can’t wait for the new features.)

But now, with the advent of XenDesktop 5, there is a new way to provision desktops: Machine Creation Services (“MCS”). As a public service to those who follow this blog, I thought I’d share Citrix’s official statement regarding MCS and KMS activation:

MCS does not support or work with KMS based Microsoft Windows 7 activation by default, however the following workaround has been provided and will be supported by Citrix Support should an issue arise.

For details on the workaround, click through the link above to the KB article.

It does not appear that there is a workaround that will allow MCS to be used with MAK activation, and I saw a comment by a Citrix employee on a forum post that indicated that there were “no plans to support it in the near future.” So…MCS with KMS, yes; MCS with MAK, no.

Not having MAK support probably isn’t a big deal, since the main reason why you would go with MAK activation rather than KMS activation would be if you had fewer than 25 desktops to activate, and if you have fewer than 25 virtual desktops, you may as well just stick with 1-to-1 images instead of messing around with provisioning anyway. But we thought you should know.

You’re welcome.

• How easy it is for a user to install the Citrix Receiver
• Self-service application delivery
• Smooth roaming (from a PC to a MacBook)
• Application streaming for off-line use
• A XenDesktop virtual desktop following the user from an HP Thin Client…
• …to an iPad…
• …as the iPad switches to 3G operation aboard a commuter train…
• …to a Mac in the home office…
• …to a Windows multi-touch PC in the kitchen…
• …to an iPhone on the golf course.
• And a demo of XenClient to wrap things up.

I remember, a few years ago, sitting through the keynote address at a Citrix conference and watching a similar video on where the technology was headed. But this isn’t smoke and mirrors, and it isn’t a presentation of some future, yet-to-be-released technology. All of this functionality is available now, and it’s all included in a single license model. The future is here. Now.

I think you’ll find that it’s 17 minutes that are well-spent:

The new trade-up program will allow XenApp users to trade up to either the user/device-based license model or the new concurrent use license model. New concurrent use licenses cost roughly 2x the cost of a user/device license. Here are the high points of the new trade-up program:

• As was the case with the earlier trade-up programs, XenApp users can choose a straight one-for-one deal, where they receive one user/device XenDesktop license for each XenApp license, or, if they trade up all of their XenApp licenses, they can choose a two-for-one deal, where they receive two user/device licenses for each XenApp license. It will just cost you a little more than it would have if you had done it before the end of 2010.
• Through the end of 2011, customers with expired Subscription Advantage can trade up their licenses for the same price as customers with current Subscription Advantage – and take advantage of the two-for-one deal. After December 31, 2011, it will cost an additional $50/license if your Subscription Advantage is expired.
• You can now choose to trade up your XenApp licenses one-for-one to XenDesktop concurrent use licenses – although it’s more expensive than trading up to user/device licenses.
• “Trade-up PLUS” – If you trade up all of your XenApp licenses, you can purchase additional XenDesktop licenses (on the same order) for 10% off the suggested retail price. These additional licenses do not have to be the same product version as the version you’re trading up to, i.e., you could trade up to XenDesktop Platinum Edition, and purchase additional XenDesktop Enterprise licenses (although I’m not sure why you’d want to).
• “Trade-up MAX” – If you trade up all of your XenApp licenses, and purchase additional XenDesktop licenses for all of your remaining users (on the same order), the additional licenses would be 35% off the suggested retail price. Again, the additional licenses do not have to be the same version as the trade-up licenses. The order must total a minimum of 2,500 XenDesktop licenses, including both the licenses received via the trade-up offer and the additional licenses. Citrix will accept data from Dun & Bradstreet or Hoovers.com, or the user count from an active Microsoft Enterprise Agreement as evidence of how many users you have.

Here is a summary of the new trade-up suggested retail prices:

Note that if your Subscription Advantage is expired, all of the prices above will go up after December 31, 2011. Note also that if you purchased XenApp Fundamentals bundled with Microsoft Terminal Services CALs, and you want to keep those Terminal Services CALs after the trade-up, you must specify that on your trade-up order. Otherwise, the Terminal services CALs will be rescinded along with the XenApp Fundamentals licenses that you’re trading up.

Citrix has provided a new Trade-Up Calculator that makes it really easy to figure out what your trade-up cost will be. You simply enter your data – how many XenApp licenses you own, how many you’re trading up, what edition your trading up from and to, whether your Subscription Advantage is current, whether you’re trading up all of your licenses, and whether you want to purchase additional licenses along with your trade-up – and the calculator will give you the various options available to you, along with the suggested retail price of each option.

You can also download a Trade-Up Brochure, and a Trade-Up FAQ Document from the Citrix Web site.

#10 – Not calculating user bandwidth requirements
Back in the “good old days” of MetaFrame, when we didn’t particularly care about 3D graphics, multimedia content, etc., we could get by with roughly 20 Kbps of network bandwidth per user session. That’s not going to cut it for a virtualized desktop, for a number of reasons that Dan outlines in his blog post. He provides the following estimates for the average bandwidth required both with and without the presence of a pair of Citrix Branch Repeaters (which have some secret sauce that is specifically designed to accelerate Citrix traffic) between the client device and the virtual desktop session:

NOTE: These are estimates – your mileage may vary!

One thing that should come across loud and clear from the table above is what a huge difference the Citrix Branch Repeater can make in your bandwidth utilization. And as we’ve always said: you only buy hardware once – bandwidth costs go on forever!

#9 – Not considering the user profile
It should go without saying that user profiles are important. But if it’s number 9 on the list of things people most often screw up, then apparently it doesn’t. In a nutshell: If you mess up the users’ profiles, the users won’t be happy – logon/logoff performance will suffer, settings (including personalization) will be lost. If the users aren’t happy, they will be extremely vocal about it, and your VDI deployment will fail for lack of user buy-in and support. There are some great tools available for managing user profiles, including the Citrix Profile Manager, and the AppSense Environment Manager. AppSense can even maintain a consistent user experience across platforms – making sure that the user profile is the same regardless of whether the user is logged onto a Windows XP system, a Windows 7 System, or a Windows Server 2008 R2-based XenApp server.

Do yourself a favor and make sure you understand what your users’ profile requirements are, then investigate the available tools and plan accordingly.

#8 – Lack of an application virtualization strategy
How many applications are actually deployed in your organization? Do you even know? Are the versions consistent across all users? Which users use which applications? You have to understand the application landscape before you can decide how you’re going to deploy applications in your new virtualized desktop environment.

You have three basic choices on how to deliver apps:

1. You can install every application into a single desktop image. That means that whenever an application changes, you have to change your base image, and do regression testing to make sure that the new or changed application didn’t break something else.
2. You can create multiple desktop images with different application sets in each image, depending on the needs of your different user groups. Now if an application changes, you may have to change and do regression testing on multiple images. It’s worth noting that many organizations have been taking this approach in managing PC desktop images for years…but part of the promise of desktop virtualization is that, if done correctly, you can break out of that cycle. But to do that, you must…
3. Remove the applications from the desktop image and deliver them some other way: either by running them on a XenApp server, or by streaming the application using either the native XenApp streaming technology or Microsoft’s App-V (or some other streaming technology of your choice).

Ultimately, you may end up with a mixed approach, where some core applications that everyone uses are installed in the desktop image, and the rest are virtualized. But, once again, it’s critical to first understand the application landscape within your organization, and then plan (and test) carefully to determine the best application delivery approach.

#7 – Improper resource allocation
Quoting Dan: “Like me, many users only consume a fraction of their total potential desktop computing power, which makes desktop virtualization extremely attractive. By sharing the resources between all users, the overall amount of required resources is reduced. However, there is a fine line between maximizing the number of users a single server can support and providing the user with a good virtual desktop computing experience.”

This post provides some great guidelines on how to optimize the environment, depending on the underlying hypervisor you’re planning to use.

#6 – Protection from Anti-Virus (as well as protection from viruses)
If you are provisioning desktops from a shared read-only image (e.g., Citrix Provisioning Services), then any virus infection will go away when the virtual PC is rebooted, because changes to the base image – including the virus – are discarded by design. But you still need AV protection, because the virus can use the interval between infection and reboot to propagate itself to other systems. The gotcha here is that the AV software itself can cause serious performance issues if it is not configured properly. Dan provides a great outline in this post for how to approach AV protection in a virtual desktop environment.

#5 – Managing the incoming storm
In most organizations, the majority of users arrive and start logging into their desktops at approximately the same time. What you don’t want is dozens, or hundreds, of virtual desktops trying to start up simultaneously, because it will hammer your virtualization environment. There are some very specific things you need to do to survive the “boot storm,” and Dan outlines them in this post.

#4 – Not optimizing the virtual desktop image
Dan provides several tips on things you should do to optimize your desktop image for the virtual environment. He also has specific sections on his blog that deal with recommended optimizations for Windows 7, and recommended optimizations for Windows XP.

#3 – Not spending your cache wisely
Specifically, we’re talking about configuring the system cache on your Provisioning Server appropriately, depending on the OS and amount of RAM in your Provisioning Server, and the type of storage repository you’re using for your vDisk(s).

#2 – Using VDI defaults
Default settings are great for getting a small Proof of Concept up and running quickly. But as you scale up your VDI environment, there are a number of things you should do. If you ignore them, performance will suffer, which means that users will be upset, which means that your VDI project is more likely to fail.

#1 – Improper storage design
This shouldn’t be a surprise, because we’ve written about this before, and even linked to a Citrix TV video of Dan discussing this very thing as part of developing a reference architecture for an SMB (under 500 desktops) deployment. We’re talking here about how to calculate the “functional IOPS” available from a given storage system, and what that means in relation to the number of IOPS a typical user will need at boot time, logon time, working hours (which will vary depending on the users themselves), and logoff time.

Just to round things out, Dan also tossed in a few “honorable mentions,” like the improper use of NIC teaming or not optimizing the NIC configuration in Provisioning Servers, trying to provision images to hardware with mismatched hardware device drivers (generally not an issue if you’re provisioning into a virtual environment), and failing to have a good business reason for launching a VDI project in the first place.

Again, this post was intended to whet your appetite by giving you enough information that you’ll want to read through Dan’s individual “top ten” posts. We would heartily recommend that you do that – you’ll probably learn a lot. (We certainly did!)