Following our launch of the new 13G-based XC series platform, I present our product architectures for the VDI-specific use cases. Of the platforms available, this use case is focused on the extremely powerful 1U XC630 with Haswell CPUs and 2133MHz RAM. We offer these appliances on both Server 2012 R2 Hyper-V and vSphere 5.5 U2 with Citrix XenDesktop, VMware Horizon View, or Dell vWorkspace.  All platform architectures have been optimized, configured for best performance and documented.

Platforms

We have three platforms to choose from optimized around cost and performance, all being ultimately flexible should specific parameters need to change. The A5 model is the most cost effective leveraging 8-core CPUs, 256GB RAM 2 x 200GB SSDs for performance and 4 x 1TB HDDs for capacity.  For POCs, small deployments or light application virtualization, this platform is well suited. The B5 model steps up the performance by adding four cores per socket, increasing the RAM density to 384GB and doubling the performance tier to 2 x 400GB SSDs. This platform will provide the best bang for the buck on medium density deployments of light or medium level workloads. The B7 is the top of the line offering 16-core CPUs and a higher capacity tier of 6 x 1TB HDDs. For deployments requiring maximum density of knowledge or power user workloads, this is the platform for you.

At 1U with dual CPUs, 24 DIMM slots and 10 drive bays…loads of potential and flexibility!

Solution Architecture

Utilizing 3 platform hardware configurations, we are offering 3 VDI solutions on 2 hypervisors. Lots of flexibility and many options. 3 node cluster minimum is required with every node containing a Nutanix Controller VM (CVM) to handle all IO. The SATADOM is present for boot responsibilities to host the hypervisor as well as initial setup of the Nutanix Home area. The SSDs and NL SAS disks are passed through directly to each CVM which straddle the hypervisor and hardware. Every CVM contributes its directly-attached disks to the storage pool which is stretched across all nodes in the Nutanix Distributed File System (NDFS) cluster. NDFS is not dependent on the hypervisor for HA or clustering. Hyper-V cluster storage pools will present SMB version 3 to the hosts and vSphere clusters will be presented with NFS. Containers can be created within the storage pool to logically separate VMs based on function. These containers also provide isolation of configurable storage characteristics in the form of dedupe and compression. In other words, you can enable compression on your management VMs within their dedicated container, but not on your VDI desktops, also within their own container. The namespace is presented to the cluster in the form of \\NDFS_Cluster_name\container_name.

The first solution I’ll cover is Dell’s Wyse vWorkspace which supports either 2012 R2 Hyper-V or vSphere 5.5. For small deployments or POCs we offer this solution in a “floating mgmt” architecture which combines the vWorkspace infrastructure management roles and VDI desktops or shared session VMs. vWorkspace and Hyper-V enables a special technology for non-persistent/ shared image desktops called Hyper-V Catalyst which includes 2 components: HyperCache and HyperDeploy. Hyper-V Catalyst provides some incredible performance boosts and requires that the vWorkspace infrastructure components communicate directly with the hyper-V hypervisor. This also means that vWorkspace does not require SCVMM to perform provisioning tasks for non-persistent desktops!

• HyperCache – Provides virtual desktop performance enhancement by caching parent VHDs in host RAM. Read requests are satisfied from cache including requests from all subsequent child VMs.
• HyperDeploy – Provides instant cloning of parent VHDs massively diminishing virtual desktop pool deployment times.

You’ll notice the HyperCache components included on the Hyper-V architectures below. 3 to 6 hosts in the floating management model, depicted below with management, desktops and RDSH VMs logically separated only from a storage container perspective by function. The recommendation of 3-7 RDSH VMs is based our work optimizing around NUMA boundaries. I’ll dive deeper into that in an upcoming post. The B7 platform is used in the architectures below.

Above ~1000 users we recommend the traditional distributed management architecture to enable more predictable scaling and performance of both the compute and management hosts. The same basic architecture is the same and scales to the full extent supported by the hypervisor, is this case Hyper-V which supports up to 64 hosts. NDFS does not have a scaling limitation so several hypervisor clusters can be built within a single contiguous NDFS namespace. Our recommendation is to then build independent Failover Clusters for compute and management discretely so they can scale up or out independently.

The architecture below depicts a B7 build on Hyper-V applicable to Citrix XenDesktop or Wyse vWorkspace.

This architecture is relatively similar for Wyse vWorkspace or VMware Horizon View on vSphere 5.5 U2 but fewer total compute hosts per HA cluster, 32 total. For vWorkspace, Hyper-V Catalyst is not present in this scenario so vCenter is required to perform desktop provisioning tasks.

For the storage containers, the best practice of less is more still stands. If you don’t need a particular feature don’t enable it, as it will consume additional resources. Deduplication is always recommended on the performance tier since the primary OpLog lives on SSD and will always benefit. Dedupe or compression on the capacity tier is not recommended, of course you absolutely need it. And if you do prepare to increase each CVM RAM allocation to 32GB.

Container	Purpose	Replication Factor	Perf Tier Deduplication	Capacity Tier Deduplication	Compression
Ds_compute	Desktop VMs	2	Enabled	Disabled	Disabled
Ds_mgmt	Mgmt Infra VMs	2	Enabled	Disabled	Disabled
Ds_rdsh	RDSH Server VMs	2	Enabled	Disabled	Disabled

Network Architecture

As a hyperconverged appliance, the network architecture leverages the converged model. A pair of 10Gb NICs minimum in  each node handle all traffic for the hypervisor, guests and storage operations between CVMs. Remember that the storage of all VMs is kept local to the host to which the VM resides, so the only traffic that will traverse the network is LAN and replication. There is no need to isolate storage protocol traffic when using Nutanix. 

Hyper-V and vSphere are functionally similar. For Hyper-V there are 2 vSwitches per host, 1 external that aggregates all of the services of the host management OS as well as the vNICs for the connected VMs. The 10Gb NICs are connected to a LBFO team configured in Dynamic Mode. The CVM alone connects to a private internal vSwitch so it can communicate with the hypervisor.

In vSphere it’s the same story but with the concept of Port Groups and vMotion.

We have tested the various configurations per our standard processes and documented the performance results which can be found in the link below. These docs will be updated as we validate additional configurations.

Product Architectures for 13G XC launch:

http://bit.ly/DellXCLib 

Resources:

About Wyse vWorkspace HyperCache

About Wyse vWorkspace HyperDeploy

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As I called out in my vSphere 5.5 upgrade post, the vSphere Client is now deprecated in 5.5 so in preparation of an inevitable future,  I’m forcing myself to use the Web Client to gain familiarity. Turns out there was way more moving around than I initially thought so I’m selfishly documenting a few pertinent items that seemed less than intuitive to me my first time through. Some things are just easier to do in the legacy vSphere Client, or maybe I’m just too accustomed after 3 generations of ESX/i. In any case, I encourage you to use the web client as well and hopefully these tips will help.

Topics covered in this post:

• How to configure iSCSI software adapters
• How to add datastores
• How to manage multipathing
• How to rename an ESXi host
• Cool changes in Recent Tasks pane
• Traffic Shaping
• Deploying vCenter Operations Manager (vCOps)

How to configure iSCSI software adapters:

This assumes that the preliminary steps of setting up your storage array and requisite physical networking have already been properly completed. The best and easiest way to do this is via dedicated switches and server NICs for iSCSI in a Layer2 switch segment. Use whatever IP scheme you like, this should be a closed fabric and there is no reason to route this traffic.

First things first, if you don’t have a software iSCSI adapter created on your hosts, create one in the Storage Adapters section of Storage Management for a particular ESXi host. Once created, it will appear in the list below. A quick note on software vs hardware iSCSI initiators. Physical initiators can generally do iSCSI offload OR jumbo frames. not both. We have seen the use of jumbo frames to be more impactful to performance than iSCSI offload, so software initiators with jumbo frames enabled is the preferred way to go here.

Click over to the Networking tab and create a new vSwitch with a VMkernel Network Adapter for iSCSI.

Choose the physical adapters to be used in this vSwitch, create a useful network Port Group label such as iSCSI-1 and assign an IP address that can reach the storage targets. Repeat this process and add a second VMkernel adapter to the same vSwitch. Configure your VMK ports to use apposing physical NICs. This is done by editing the port group settings and changing the Failover order. This allows you to cleanly share 2 physical NICs for 2 iSCSI connections within a single vSwitch.

In my case VMK2 is active on vmnic3 and VMK3 is active on vmnic1 providing physical path redundancy to the storage array.

When all is said and done, your vSwitch configuration should look something like this:

Next under the iSCSI software adapter, add the target IP to your storage (group IP for EqualLogic). Authentication needs and requirements will vary between organizations. Choose and configure this scheme appropriately for your environment. For my lab, I scope connections based on subnet alone which defines the physical Layer2 boundary of my iSCSI fabrics.

Next configure the network port binding to ensure that the port groups you defined earlier get bound to the iSCSI software adapter using the proper physical interfaces.

At this point, if you have any volumes created on your array and presented to your host, a quick rescan should reveal the devices presented to your host as LUNs.

You should also see 2 paths per LUN (device) per host based on 2 physical adapters connecting to your array. EqualLogic is an active/passive array so only connections to the active controller will be seen here.

If you run into trouble making this work after these steps, jump over to the vSphere Client which does make this process a bit easier. Also keep in mind that all pathing will be set to Fixed by default. See my How to manage multipathing topic below for guidance on changing this.

iSCSI works very well with jumbo frames which is an end-to-end Layer2 technology, so makes sure a MTU of 9000 is set on all ESXi iSCSI vSwitches, VMK ports, as well as the NICs on the storage array. Your switches must be capable of supporting jumbo frames as well. This will increase the performance of your iSCSI network and front-end storage operation speeds.

 

How to add datastores:

Once your new datastore has been provisioned from your storage platform and presented to your ESXi hosts, from the Hosts and Clusters view, navigate to Related Objects then datastores. From here click the Create a new Datastore button.

Choose the host or cluster to add the datastore to, choose whether it is NFS or VMFS, name the datastore and choose a host that can see it. You should see the raw LUN in the dialog below.

Choose the VMFS version and any partition options you want to implement. Confirm and deploy.

If presenting to multiple hosts, once the VMFS datastore is created and initialized on one, they all should see it assuming the raw device is present via a previous adapter rescan.

 

How to manage multipathing:

From the Hosts and clusters view, click the Storage tab, choose the datastore you want to manage, click Manage in the middle pane then click Connectivity and Multipathing under Settings.

Alternatively, from the Hosts and Clusters view (from any level item), navigate to Related Objects, then Datastores. Either click the volume you want to edit or choose Settings from the dropdown. Either method will get you to the same place.

From the datastore Settings page, click Manage and under Settings (once again) click Connectivity and Multipathing. In the middle of the screen you should see all hosts attached to whatever datastore you selected. Clicking on each host will reveal the current Path Selection Policy below, “Fixed” by VMware default along with the number of paths present per host.

To change this to Round Robin, click Edit Multipathing, change the Path Selection Policy, repeat for each host connected to the datastore.

 

How to rename an ESXi host:

Renaming hosts is one area that the Web Client has made significantly easier (once you figure out where to go)! Select a host from the Hosts and Clusters view, click Manage, click Networking, then TCP/IP Configuration below.

From the DNS Configuration menu, select “Enter settings manually”, put whatever hostname you would like here.

VMware recommends putting a host in maintenance mode and disconnecting it from vCenter before doing this. I did this hot with my host active in an HA cluster with zero ill affects. I did it a few times just to make sure. The other way to do this is via the CLI. Connect to your ESXi host via SSH, vMA or vCLI and run:

esxcli system hostname set --host=hostname

Cool changes in Recent Tasks pane:

Not only is the Recent Tasks pane off to the right now, which I really like, it breaks out tasks by All, Running and Failed individually for easier viewing, including the ability to view your own tasks for environments with many admins. Previously these tasks were all lumped together and longer running tasks would get buried in the task stream.

 

The Recent Tasks pane also provides a new and better method to deal with pop-up configuration dialogs. Ever start configuring something using the old vSphere Client, get 4-5 clicks deep in the pop-up configuration, then realize you need some other piece of information requiring you to cancel out so you can go back to some other area in vCenter? This problem is now resolved in the web client with a cool new section of the Tasks pane called Work in Progress. It doesn’t matter what you’re doing or how far along you are in the dialog. If you need to break away for any reason, you can simply minimize the pop up and come back to it later. These minimized pop-ups will show in the Work in Progress pane below recent tasks.

The example here shows 3 concurrent activities in various states: a vMotion operation, a VM edit settings and a clone operation of the same VM even. Any activity that generates a pop-up dialog can be set aside and picked up again later. This is a huge improvement over the legacy vSphere Client. Very cool!!

 

Traffic Shaping:

It appears that in the web client you can only apply traffic shaping at the vSwitch level, not at an individual port group or VMK level. Here you can see shaping available for the standard vSwitch:

These settings, while viewable in the VMK policies summary, are not changeable (that I can see).

To override the vSwitch shaping policy and apply one to an individual port group or VMK, you have to use the legacy vSphere Client. Not sure if this is an oversight on VMware’s part or yet another sign of things to come requiring dvSwitching to assign shaping policies below the vSwitch level.

 

Deploying vCenter Operations Manager (vCOps):

Made extremely easy in vSphere 5.5 via the web client is the deployment of the incredible vCOps vApp for advanced monitoring of your environment. VMware has made detailed performance monitoring of your vSphere world incredibly simply and intuitive through this easy to set up and use vApp. Really impressive. From the home page, click vCenter Operations Management.

On the Getting Started screen, click Deploy vCOps. If you have a valid vmware.com login, entire it here to download the OVF and related files for deployment. You can alternatively point to the file locally if you have it already.

Accept the EULAs and choose all the placement and sizing options for the VM.

A word of caution, do not expect DRS to make a host placement decision for you here during the deployment. The wizard will allow you to select your cluster as a resource destination but the deployment will ultimately fail. Choose a specific host to deploy the VM to instead.

The requisite files will be downloaded from VMware directly and deployed to your environment. Off to the races!

Once deployed, you’ll see 2 new VMs running under the vCOps vApp object in your datacenter.

Once the VMs are powered on and the vApp has been started, you should see new options under vCenter Operations Manager.

First, click the Configure link to open the admin site in a web page. The default login for the admin account is admin/ admin, for root the password is vmware. Configure the initial setup to point to vCenter and the analytics VM which it should detect. Install the certificates as prompted and continue through the registration process.

Once complete, return to the vCOps page in vCenter and click Open, a new web page will launch for you to consume the vCOps goodness. After a short while performance stats should start pouring in for everything in your vSphere environment. Usage patterns and workload profiles can be identified so appropriate adjustments can be made. What you do from here with the data collected is entirely up to you. :-)

A couple more screens just to show you the capability of vCOps, since I like it so much. Storage at the datastore view:

VM performance view:

[This post references portions of published test results from various Dell DVS Enterprise reference architectures. We design, build, test and publish E2E enterprise VDI architectures, SKU’d and sold globally. Head over here and have a look for more information.]
There are four core elements that we typically focus on for performance analysis of VDI: CPU, memory, disk, and network. Each plays a uniquely integral role in the system overall with the software in play defining how each element is consumed and to what extent. In this post I’ll go over some of the key considerations when planning an enterprise VDI infrastructure.

CPU

First things first, no matter what you’ve heard or read, the primary VDI bottleneck is CPU. We in CCC/ DVS at Dell prove this again and again, across all hypervisors, all brokers and any hardware configuration. There are special use case caveats to this of course, but generally speaking, your VDI environment will run out of compute CPU before it runs out of anything else! CPU is a finite shared resource unlike memory, disk or network which can all be incrementally increased or adjusted. There are many special purpose vendors and products out there that will tell you the VDI problem is memory or IOPS, those can be issues but you will always come back to CPU.
Intel’s Ivy Bridge is upon us now, delivering more cores at higher clocks with more cache and supporting faster memory. It is decidedly cheaper to purchase a more expensive pair of CPUs then it is to purchase an entire additional server. For that reason, we recommend running [near] top bin CPUs in your compute hosts as we see measurable benefit in running faster chips. For management hosts you can get by with a lower spec CPU but if you want to get the best return on investment for your compute hosts and get as many users as you can per host, buy the fast CPUs! Our recommendation in DVS enterprise will be following the lateral succession to Ivy Bridge from the Sandy Bridge parts we previously recommended: Xeon E5-2690v2 (IB) vs E5-2690 (SB). 
The 2690v2 is a 10 core part using a 22nm process with a 130w TDP clocking in at 3.0GHz and supporting up to 1866MHz DDR3 memory. We tested the top of the line E5-2697v2 (12 cores) as well as the faster 1866MHz memory and saw no meaningful improvement in either case to warrant a core recommendation. It’s all about the delicate balance of the right performance for the right price.
There is no 10c part in the AMD Opteron 6300 line so the closest competitor is the Opteron 6348 (Piledriver). As has always been the case, the AMD parts are a bit cheaper and run more efficiently. AMD clocks lower (with turbo) and due to no hyperthreading feature, executes fewer simultaneous threads. The 6348 also only supports 1600MHz memory but provides a few additional instruction sets. Both run 4 memory channels with an integrated memory controller. AMD also offers a 16c part at its top end in the 6386SE. I have no empirical data on AMD vs Intel for VDI at this time.
Relevant CPU spec comparison, our default selection for DVS Enterprise highlighted in red:

Performance analysis:

To drive this point home regarding the importance of CPU in VDI, here are 2 sets of test results published in my reference architecture for DVS Enterprise on XenDesktop, one on vSphere, one of Hyper-V, both based on Sandy Bridge (we haven’t published our Ivy Bridge data yet). MCS vs PVS is another discussion entirely but in either case, CPU is always the determining factor of scale. These graphs are based on tests using MCS and R720’s fitted with 2 x E5-2690 CPUs and 192GB RAM running the LoginVSI Light workload.
Hyper-V:
The 4 graphs below tell the tale fairly well for 160 concurrent users. Hyper-V does a very good job of optimizing CPU while consuming slightly higher amounts of other resources. Network consumption, while very reasonable and much lower than you might expect for 160 users, is considerably larger than in the vSphere use case in the next example. Once steady state has been reached, CPU peaks right around 85% which is the generally accepted utilization sweet spot making the most of your hardware investment while leaving head room for unforeseen spikes or temporary resource consumption. Memory in use is on the high side given the host had 192GB, but that can be easily remedied by raising to 256GB. 

vSphere:

Similar story for vSphere, although the user density below is representative of only 125 desktops of the same user workload. This speaks to another trend we are seeing more and more of which is a stark CPU performance reduction of vSphere compared to Hyper-V for non-View brokers. 35 fewer users overall here but disk performance is also acceptable. In the example below, CPU spikes slightly above 85% at full load with disk performance and network consumption well within reasonable margins. Where vSphere really shines is in it’s memory management capabilities thanks to features the likes of Transparent Page Sharing, as you can see the active memory is quite a bit lower than what has actually been assigned.

Are 4 sockets better than 2?

Not necessarily. 4-socket servers, such as the Dell PowerEdge R820, use a different mutli-processor (MP) CPU architecture, currently based on Sandy Bridge EP (E5-4600 family) versus the dual processor (DP) CPU architectures of its dual socket server counterparts.  MP CPUs and their 4-socket servers are inherently more expensive, especially considering the additional RAM required to run whatever additional user densities. 2 additional CPUs does not mean twice the user density in a 4-socket platform either!  A similarly configured 2-socket server is roughly half the cost of a 4-socket box and it is for this reason that we recommend the Dell PowerEdge R720 for DVS Enterprise. You will get more users on 2 x R720s cheaper than if you ran a single R820.

Memory

Memory architecture is an important consideration for any infrastructure planning project. Our experience shows that VDI appears to be less sensitive to memory bandwidth performance than other enterprise applications. Besides overall RAM density per host, DIMM speed and loading configuration are important considerations. In Sandy and Ivy Bridge CPUs, there are 4 memory channels, 3 DIMM slots each, per CPU (12 slots total). Your resulting DIMM clock speed and total available bandwidth will vary depending on how you populate these slots.

As you can see from the table below, loading all slots on a server via 3 DPC (3 DIMMs per channel) will result in a forced clock reduction to either 1066 or 1333 depending on the DIMM voltage. If you desire to run at 1600MHz or 1866Mhz (Ivy) you cannot populate the 3rd slot per channel which will net 8 empty DIMM slots per server. You’ll notice that the higher memory clocks are also achievable using lower voltage RDIMMs.

Make sure to always use the same DIMM size, clock and slot loading to ensure a balanced configuration. To follow the example of 256GB in a compute host, the proper loading to maintain maximum clock speeds and 4-channel bandwidth is as follows per CPU:

If 256GB is not required, leaving the 4th channel empty is also acceptable in “memory optimized” BIOS mode although it does reduce the overall memory bandwidth by 25%. In our tests with the older sandy bridge E5-2690 CPUs, we did not find that this affected desktop VM performance.

Disk

There are 3 general considerations for storage that vary depending on the requirements of the implementation: capacity, performance and protocol.
Usable capacity must be sufficient to meet the needs of both Tier1 and Tier2 storage requirements which will differ greatly based on persistent or non-persistent desktops. We generally see an excess of usable capacity as a result of the number of disks required to provide proper performance. This of course is not always the case as bottlenecks can often arise in other areas, such as array controllers. It is less expensive to run RAID10 in fewer arrays to achieve a given performance requirement, than it is to run more arrays at RAID50. Sometimes you need to maximize capacity, sometimes you need to maximize performance. Persistent desktops (full clones) will consume much more disk than their non-persistent counterparts so additional storage capacity can be purchased or a deduplication technology can be leveraged to reduce the amount of actual disk required. If using local disk, in a Local Tier 1 solution model, inline dedupe software can be implemented to reduce the amount of storage required by several fold. Some shared storage arrays have this capability built in. Other solutions, such as Microsoft’s native dedupe capability in Server 2012 R2, make use of file servers to host Hyper-V VMs via SMB3 to reduce the amount of storage required.
Disk performance is another deep well of potential and caveats again related directly to the problems one needs to solve.  A VDI desktop can consume anywhere from 3 to over 20 IOPS for steady state operation depending on the use case requirements. Sufficient steady state disk performance can be provided without necessarily solving the problems related to boot or login storms (many desktop VMs being provisioned/ booted or many users logging in all at once). Designing a storage architecture to withstand boot or login storms requires providing a large amount of available IOPS capability which can be via hardware or software based solutions, neither generally inexpensive. Some products combine the ability to provide high IOPS while also providing dedupe capabilities. Generally speaking, it is much more expensive to provide high performance for potential storms than it is to provide sufficient performance for normal steady state operations. When considering SSDs and shared storage, one needs to be careful to consider the capabilities of the array’s controllers which will almost always exhaust before the attached disk will. Just because you have 50K IOPS potential in your disk shelves on the back end, does not mean that the array is capable of providing that level of performance on the front end!
There is not a tremendous performance difference between storage protocols used to access a shared array on the front end, this boils down to preference these days. Fiber Channel has been proven to outperform iSCSI and file protocols (NFS) by a small margin but performance alone is not really reason enough to choose between them. Local disk also works well but concessions may need to be made with regard to HA and VM portability. Speed, reliability, limits/ maximums, infrastructure costs and features are key considerations when deciding on a storage protocol. At the end of the day, any of these methods will work well for an enterprise VDI deployment. What features do you need and how much are you willing to spend?

Network

Network utilization is consistently (and maybe surprisingly) low, often in the Kbps/ per user. VDI architectures in and of themselves simply don’t drive a ton of steady network utilization. VDI is bursty and will exhibit higher levels of consumption during large aggregate activities such as provisioning or logins. Technologies like Citrix Provisioning Server will inherently drive greater consumption by nature. What will drive the most variance here is much more reliant on upstream applications in use by the enterprise and their associated architectures. This is about as subjective as it gets, so impossible to speculate in any kind of fashion across the board. Now you will have a potentially high number of users on a large number of hosts, so comfortable network oversubscription planning should be done to ensure proper bandwidth in and out of the compute host or blade chassis. Utilizing enterprise-class switching components that are capable of operating at line rates for all ports is advisable. Will you really need hundreds of gigs of bandwidth? I really doubt it. Proper HA is generally desirable along with adherence to sensible network architectures (core/ distribution, leaf/spline). I prefer to do all of my routing at the core leaving anything Layer2 at the Top of Rack. Uplink to your core or distribution layers using 10Gb links which can be copper (TwinAx) for shorter runs or fiber for longer runs.

In Closing

That about sums it up for the core 4 performance elements. To put a bow on this, hardware utilization analysis is fine and definitely worth doing, but user experience is ultimately what’s important here. All components must sing together in harmony to provide the proper level of scale and user experience. A combination of subjective and automated monitoring tests during a POC will give a good indication of what users will experience.  At Dell, we use Stratusphere UX by Liquidware Labs to measure user experience in combination with Login Consultants LoginVSI for load generation. A personal, subjective test (actually log in to a session) is always a good idea when putting your environment under load, but a tool like Stratusphere UX can identify potential pitfalls that might otherwise go unnoticed.
Keeping tabs on latencies, queue lengths and faults, then reporting each users’ experience into a magic-style quadrant will give you the information required to ascertain if your environment will either perform as designed, or send you scrambling to make adjustments.