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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I am pleased to present the Dell XC 2.0 series of web-scale appliances based on the award-winning 13G PowerEdge server line from Dell. There’s lots more in store for the XC so just focusing on this part of the launch we are introducing the XC630 and the XC730xd appliances.

Flexibility and performance are key tenets of this launch providing not only a choice in 1U or 2U form factors, but an assortment of CPU and disk options. From a solution perspective, specifically around VDI, we are releasing three optimized and validated platforms with accompanied Product Architectures to help you plan and size your Dell XC deployments.

The basic architecture of the Dell XC powered by Nutanix remains the same. Every node is outfitted with a Nutanix Controller VM (CVM) that connects to a mix of SSD and HDD to contribute to a distributed storage pool that has no inherent scaling limitation. Three nodes minimum required and either VMware vSphere or Microsoft Windows Server 2012 R2 Hyper-V are supported hypervisors. Let’s take a look at the new models.

XC630

The XC630 is a 1U dual-socket platform that supports 6-core to 16-core CPUs and up to 24 x 2133MHz 16GB RDIMMs or 32GB LRDIMMs. The XC630 can be configured using all flash or using two tiers of storage which can consist of 2 to 4 x SSDs (200GB, 400GB or 800GB) and 4 to 8 x 1TB HDDs (2TB HDDs coming soon). Flexible! All flash nodes must have a minimum of 6 x SSDs while nodes with two storage tiers must have a minimum of two SSDs and four HDDs. All nodes have a minimum of 2 x 1Gb plus 2 x 10Gb SFP+ or BaseT Ethernet that can be augmented via an additional card.

New to the XC 2.0 series is a 64GB SATADOM that is used to boot each node. Each node is also outfitted with a 16GB SD card used for the purposes of initial deployment and recovery. The SSDs and HDDs that comprise the Nutanix Distributed File System (NDFS) storage pool are presented to each CVM via an on-board 1GB PERC H730 set in pass-through mode. Simple, powerful, flexible.

 

XC730xd

For deployments requiring a greater amount of cold tier data capacity, the XC730xd can provide up to 32TB raw per node. The XC730xd is a 2U dual-socket platform that supports 6-core to 16-core CPUs and up to 24 x 2133MHz 16GB RDIMMs or 32GB LRDIMMs. The XC730xd is provided with two chassis options: 24 x 2.5” disks or 12 x 3.5” disks. The 24-drive model requires the use of two tiers of storage which can consist of 2 to 4 x SSDs (200GB, 400GB or 800GB) and 4 to 22 x 1TB HDDs .The 12-drive model also requires two tiers of storage consisting of 2 to 4 x SSDs (200, 400GB or 800GB) and up to 10 x 4TB HDDs. All nodes have a minimum of 2 x 1Gb plus 2 x 10Gb SFP+ or BaseT Ethernet that can be augmented via an additional card.

The XC730xd platforms are also outfitted with a 64GB SATADOM that is used to boot the nodes. The 16GB SD card used for the purposes of initial deployment and recovery is present on these models as well. The SSDs and HDDs that comprise the Nutanix Distributed File System (NDFS) storage pool are presented to each CVM via an on-board 1GB PERC H730 set in pass-through mode. Simple, powerful, flexible.

12 drive option, hopefully the overlaps in the image below make sense:

 

24 drive option:

 

Nutanix Software Editions

All editions of the Nutanix software platform are available with variable lengths for support and maintenance.

This is just the beginning. Keep an eye out for additional platforms and offerings from the Dell + Nutanix partnership! Next up is the VDI product architectures based on the XC630. Stay tuned!!

http://www.dell.com/us/business/p/dell-xc-series/pd

If you’re unfamiliar, PVS (Citrix Provisioning Server) is a vDisk deployment mechanism available for use within a XenDesktop or XenApp environment that uses streaming for image delivery. Shared read-only vDisks are streamed to virtual or physical targets in which users can access random pooled or static desktop sessions. Random desktops are reset to a pristine state between logoffs while users requiring static desktops have their changes persisted within a Personal vDisk pinned to their own desktop VM. Any changes that occur within the duration of a user session are captured in a write cache. This is where the performance demanding write IOs occur and where PVS offers a great deal of flexibility as to where those writes can occur. Write cache destination options are defined via PVS vDisk access modes which can dramatically change the performance characteristics of your VDI deployment. While PVS does add a degree of complexity to the overall architecture, since its own infrastructure is required, it is worth considering since it can reduce the amount of physical computing horsepower required for your VDI desktop hosts. The following diagram illustrates the relationship of PVS to Machine Creation Services (MCS) in the larger architectural context of XenDesktop. Keep in mind also that PVS is frequently used to deploy XenApp servers as well.

PVS 7.1 supports the following write cache destination options (from Link):

• Cache on device hard drive - Write cache can exist as a file in NTFS format, located on the target-device’s hard drive. This write cache option frees up the Provisioning Server since it does not have to process write requests and does not have the finite limitation of RAM.
• Cache on device hard drive persisted (experimental phase only) - The same as Cache on device hard drive, except cache persists. At this time, this write cache method is an experimental feature only, and is only supported for NT6.1 or later (Windows 7 and Windows 2008 R2 and later).
• Cache in device RAM - Write cache can exist as a temporary file in the target device’s RAM. This provides the fastest method of disk access since memory access is always faster than disk access.
• Cache in device RAM with overflow on hard disk - When RAM is zero, the target device write cache is only written to the local disk. When RAM is not zero, the target device write cache is written to RAM first.
• Cache on a server - Write cache can exist as a temporary file on a Provisioning Server. In this configuration, all writes are handled by the Provisioning Server, which can increase disk IO and network traffic.
• Cache on server persistent - This cache option allows for the saving of changes between reboots. Using this option, after rebooting, a target device is able to retrieve changes made from previous sessions that differ from the read only vDisk image.

Many of these were available in previous versions of PVS, including cache to RAM, but what makes v7.1 more interesting is the ability to cache to RAM with the ability to overflow to HDD. This provides the best of both worlds: extreme RAM-based IO performance without the risk since you can now overflow to HDD if the RAM cache fills. Previously you had to be very careful to ensure your RAM cache didn’t fill completely as that could result in catastrophe. Granted, if the need to overflow does occur, affected user VMs will be at the mercy of your available HDD performance capabilities, but this is still better than the alternative (BSOD).

Results

Even when caching directly to HDD, PVS shows lower IOPS/ user numbers than MCS does on the same hardware. We decided to take things a step further by testing a number of different caching options. We ran tests on both Hyper-V and ESXi using our standard 3 user VM profiles against LoginVSI’s low, medium, high workloads. For reference, below are the standard user VM profiles we use in all Dell Wyse Datacenter enterprise solutions:

 

Profile Name	Number of vCPUs per Virtual Desktop	Nominal RAM (GB) per Virtual Desktop	Use Case
Standard	1	2	Task Worker
Enhanced	2	3	Knowledge Worker
Professional	2	4	Power User

We tested three write caching options across all user and workload types: cache on device HDD, RAM + Overflow (256MB) and RAM + Overflow (512MB). Doubling the amount of RAM cache on more intensive workloads paid off big netting a near host IOPS reduction to 0. That’s almost 100% of user generated IO absorbed completely by RAM. We didn’t capture the IOPS generated in RAM here using PVS, but as the fastest medium available in the server and from previous work done with other in-RAM technologies, I can tell you that 1600MHz RAM is capable of tens of thousands of IOPS, per host. We also tested thin vs thick provisioning using our high end profile when caching to HDD just for grins. Ironically, thin provisioning outperformed thick for ESXi, the opposite proved true for Hyper-V. To achieve these impressive IOPS number on ESXi it is important to enable intermediate buffering (see links at the bottom). I’ve highlighted the more impressive RAM + overflow results in red below. Note: IOPS per user below indicates IOPS generation as observed at the disk layer of the compute host. This does not mean these sessions generated close to no IOPS.

Hyper-visor	PVS Cache Type	Workload	Density	Avg CPU %	Avg Mem Usage GB	Avg IOPS/User	Avg Net KBps/User
ESXi	Device HDD only	Standard	170	95%	1.2	5	109
ESXi	256MB RAM + Overflow	Standard	170	76%	1.5	0.4	113
ESXi	512MB RAM + Overflow	Standard	170	77%	1.5	0.3	124
ESXi	Device HDD only	Enhanced	110	86%	2.1	8	275
ESXi	256MB RAM + Overflow	Enhanced	110	72%	2.2	1.2	284
ESXi	512MB RAM + Overflow	Enhanced	110	73%	2.2	0.2	286
ESXi	HDD only, thin provisioned	Professional	90	75%	2.5	9.1	250
ESXi	HDD only thick provisioned	Professional	90	79%	2.6	11.7	272
ESXi	256MB RAM + Overflow	Professional	90	61%	2.6	1.9	255
ESXi	512MB RAM + Overflow	Professional	90	64%	2.7	0.3	272

For Hyper-V we observed a similar story and did not enabled intermediate buffering at the recommendation of Citrix. This is important! Citrix strongly recommends to not use intermediate buffering on Hyper-V as it degrades performance. Most other numbers are well inline with the ESXi results, save for the cache to HDD numbers being slightly higher.

Hyper-visor	PVS Cache Type	Workload	Density	Avg CPU %	Avg Mem Usage GB	Avg IOPS/User	Avg Net KBps/User
Hyper-V	Device HDD only	Standard	170	92%	1.3	5.2	121
Hyper-V	256MB RAM + Overflow	Standard	170	78%	1.5	0.3	104
Hyper-V	512MB RAM + Overflow	Standard	170	78%	1.5	0.2	110
Hyper-V	Device HDD only	Enhanced	110	85%	1.7	9.3	323
Hyper-V	256MB RAM + Overflow	Enhanced	110	80%	2	0.8	275
Hyper-V	512MB RAM + Overflow	Enhanced	110	81%	2.1	0.4	273
Hyper-V	HDD only, thin provisioned	Professional	90	80%	2.2	12.3	306
Hyper-V	HDD only thick provisioned	Professional	90	80%	2.2	10.5	308
Hyper-V	256MB RAM + Overflow	Professional	90	80%	2.5	2.0	294
Hyper-V	512MB RAM + Overflow	Professional	90	79%	2.7	1.4	294

Implications

So what does it all mean? If you’re already a PVS customer this is a no brainer, upgrade to v7.1 and turn on “cache in device RAM with overflow to hard disk” now. Your storage subsystems will thank you. The benefits are clear in both ESXi and Hyper-V alike. If you’re deploying XenDesktop soon and debating MCS vs PVS, this is a very strong mark in the “pro” column for PVS. The fact of life in VDI is that we always run out of CPU first, but that doesn’t mean we get to ignore or undersize for IO performance as that’s important too. Enabling RAM to absorb the vast majority of user write cache IO allows us to stretch our HDD subsystems even further, since their burdens are diminished. Cut your local disk costs by 2/3 or stretch those shared arrays 2 or 3x. PVS cache in RAM + overflow allows you to design your storage around capacity requirements with less need to overprovision spindles just to meet IO demands (resulting in wasted capacity).

References:

DWD Enterprise Reference Architecture

http://support.citrix.com/proddocs/topic/provisioning-7/pvs-technology-overview-write-cache-intro.html 

When to Enable Intermediate Buffering for Local Hard Drive Cache

Peter Fine here from Dell CCC Solution Engineering, where we just finished an extensive refresh for our XenApp recommendation within the Dell Wyse Datacenter for Citrix solution architecture.  Although not called “XenApp” in XenDesktop versions 7 and 7.1 of the product, the name has returned officially for version 7.5. XenApp is still architecturally linked to XenDesktop from a management infrastructure perspective but can also be deployed as a standalone architecture from a compute perspective. The best part of all now is flexibility. Start with XenApp or start with XenDesktop then seamlessly integrate the other at a later time with no disruption to your environment. All XenApp really is now, is a Windows Server OS running the Citrix Virtual Delivery Agent (VDA). That’s it! XenDesktop on the other hand = a Windows desktop OS running the VDA.

Architecture

The logical architecture depicted below displays the relationship with the two use cases outlined in red. All of the infrastructure that controls the brokering, licensing, etc is the same between them. This simplification of architecture comes as a result of XenApp shifting from the legacy Independent Management Architecture (IMA) to XenDesktop’s Flexcast Management Architecture (FMA). It just makes sense and we are very happy to see Citrix make this move. You can read more about the individual service components of XenDesktop/ XenApp here.

Expanding the architectural view to include the physical and communication elements, XenApp fits quite nicely with XenDesktop and compliments any VDI deployment. For simplicity, I recommend using compute hosts dedicated to XenApp and XenDesktop, respectively, for simpler scaling and sizing. Below you can see the physical management and compute hosts on the far left side with each of their respective components considered within. Management will remain the same regardless of what type of compute host you ultimately deploy but there are several different deployment options. Tier 1 and tier 2 storage are comprehended the same way when XenApp is in play, which can make use of local or shared disk depending on your requirements. XenApp also integrates nicely with PVS which can be used for deployment and easy scale out scenarios.  I have another post queued up for PVS sizing in XenDesktop.

From a stack view perspective, XenApp fits seamlessly into an existing XenDesktop architecture or can be deployed into a dedicated stack. Below is a view of a Dell Wyse Datacenter stack tailored for XenApp running on either vSphere or Hyper-v using local disks for Tier 1. XenDesktop slips easily into the compute layer here with our optimized host configuration. Be mindful of the upper scale utilizing a single management stack as 10K users and above is generally considered very large for a single farm. The important point to note is that the network, mgmt and storage layers are completely interchangeable between XenDesktop and XenApp. Only the host config in the compute layer changes slightly for XenApp enabled hosts based on our optimized configuration.

Use Cases

There are a number of use cases for XenApp which ultimately relies on Windows Server’s RDSH role (terminal services). The age-old and most obvious use case is for hosted shared sessions, i.e. many users logging into and sharing the same Windows Server instance via RDP. This is useful for managing access to legacy apps, providing a remote access/ VPN alternative, or controlling access to an environment through which can only be accessed via the XenApp servers. The next step up naturally extends to application virtualization where instead of multiple users being presented with and working from a full desktop, they simply launch the applications they need to use from another device. These virtualized apps, of course, consume a full shared session on the backend even though the user only interacts with a single application. Either scenario can now be deployed easily via Delivery Groups in Citrix Studio.

XenApp also compliments full XenDesktop VDI through the use of application off-load. It is entirely viable to load every application a user might need within their desktop VM, but this comes at a performance and management cost. Every VDI user on a given compute host will have a percentage of allocated resources consumed by running these applications which all have to be kept up to date and patched unless part of the base image. Leveraging XenApp with XenDesktop provides the ability to off-load applications and their loads from the VDI sessions to the XenApp hosts. Let XenApp absorb those burdens for the applications that make sense. Now instead of running MS Office in every VM, run it from XenApp and publish it to your VDI users. Patch it in one place, shrink your gold images for XenDesktop and free up resources for other more intensive non-XenApp friendly apps you really need to run locally. Best of all, your users won’t be able to tell the difference!

Optimization

We performed a number of tests to identify the optimal configuration for XenApp. There are a number of ways to go here: physical, virtual, or PVS streamed to physical/ virtual using a variety of caching options. There are also a number of ways in which XenApp can be optimized. Citrix wrote a very good blog article covering many of these optimization options, of which most we confirmed. The one outlier turned out to be NUMA where we really didn’t see much difference with it turned on or off. We ran through the following test scenarios using the core DWD architecture with LoginVSI light and medium workloads for both vSphere and Hyper-V:

• Virtual XenApp server optimization on both vSphere and Hyper-V to discover the right mix of vCPUs, oversubscription, RAM and total number of VMs per host
• Physical Windows 2012 R2 host running XenApp
• The performance impact and benefit of NUMA enabled to keep the RAM accessed by a CPU local to its adjacent DIMM bank.
• The performance impact of various provisioning mechanisms for VMs: MCS, PVS write cache to disk, PVS write cache to RAM
• The performance impact of an increased user idle time to simulate a less than 80+% concurrency of user activity on any given host.

To identify the best XenApp VM config we tried a number of configurations including a mix of 1.5x CPU core oversubscription, fewer very beefy VMs and many less beefy VMs. Important to note here that we based on this on the 10-core Ivy Bridge part E5-2690v2 that features hyperthreading and Turbo boost. These things matter! The highest density and best user experience came with 6 x VMs each outfitted with 5 x vCPUs and 16GB RAM.  Of the delivery methods we tried (outlined in the table below), Hyper-V netted the best results regardless of provisioning methodology. We did not get a better density between PVS caching methods but PVS cache in RAM completely removed any IOPS generated against the local disk. I’ll got more into PVS caching methods and results in another post.

Interestingly, of all the scenarios we tested, the native Server 2012 R2 + XenApp combination performed the poorest. PVS streamed to a physical host is another matter entirely, but unfortunately we did not test that scenario. We also saw no benefit from enabling NUMA. There was a time when a CPU accessing an adjacent CPU’s remote memory banks across the interconnect paths hampered performance, but given the current architecture in Ivy Bridge and its fat QPIs, this doesn’t appear to be a problem any longer.

The “Dell Light” workload below was adjusted to account for less than 80% user concurrency where we typically plan for in traditional VDI. Citrix observed that XenApp users in the real world tend to not work all at the same time. Less users working concurrently means freed resources and opportunity to run more total users on a given compute host.

The net of this study shows that the hypervisor and XenApp VM configuration matter more than the delivery mechanism. MCS and PVS ultimately netted the same performance results but PVS can be used to solve other specific problems if you have them (IOPS).

* CPU % for ESX Hosts was adjusted to account for the fact that Intel E5-2600v2 series processors with the Turbo Boost feature enabled will exceed the ESXi host CPU metrics of 100% utilization. With E5-2690v2 CPUs the rated 100% in ESXi is 60000 MHz of usage, while actual usage with Turbo has been seen to reach 67000 MHz in some cases. The Adjusted CPU % Usage is based on 100% = 66000 MHz usage and is used in all charts for ESXi to account for Turbo Boost. Windows Hyper-V metrics by comparison do not report usage in MHz, so only the reported CPU % usage is used in those cases.

** The “Dell Light” workload is a modified VSI workload to represent a significantly lighter type of user. In this case the workload was modified to produce about 50% idle time.

†Avg IOPS observed on disk is 0 because it is offloaded to RAM.

Summary of configuration recommendations:

• Enable Hyper-Threading and Turbo for oversubscribed performance gains.
• NUMA did not show to have a tremendous impact enabled or disabled.
• 1.5x CPU oversubscription per host produced excellent results. 20 physical cores x 1.5 oversubscription netting 30 logical vCPUs assigned to VMs.
• Virtual XenApp servers outperform dedicated physical hosts with no hypervisor so we recommend virtualized XenApp instances.
• Using 10-Core Ivy Bridge CPUs, we recommend running 6 x XenApp VMs per host, each VM assigned 5 x vCPUs and 16GB RAM.
• PVS cache in RAM (with HD overflow) will reduce the user IO generated to disk almost nothing but may require greater RAM densities on the compute hosts. 256GB is a safe high water mark using PVS cache in RAM based on a 21GB cache per XenApp VM.

Resources:

Dell Wyse Datacenter for Citrix – Reference Architecture

XenApp/ XenDesktop Core Concepts

Citrix Blogs – XenApp Scalability

Dell DVS Enterprise is now Dell Wyse Datacenter (DWD) and with the brand change we are proud to announce the 6th release of our flagship set of enterprise VDI solutions for Citrix XenDestop. Dell Wyse Datacenter is the only true end to end (E2E) VDI solution suite in the industry providing best of breed hardware and software for any size enterprise. What makes Dell different is that we carefully vet, craft and test our solutions using real-world requirements and workloads making it easier for customers to adopt our solutions. Dell Wyse Datacenter includes a number of platform and scaling options to meet almost any need: rack, blade, local disk, iSCSI, fiber channel, low cost, high performance, high scale…we have a validated and proven answer to solve your VDI business problem.

The full DWD reference architectures for Citrix can be found here:

Core RA

VRTX RA

Graphics RA

New in DWD 6th release:

• Citrix XenDesktop 7.1 support
• Support for Dell EqualLogic PS6210 series
• Dell Wyse Cloud Client updates
• High performance SAN-less blade offering
• Support for LoginVSI 4
• High IOPS persistent desktops using Atlantis ILIO: Link
• Citrix vGPU support for graphical acceleration

Citrix XenDesktop 7.1

Architecturally, Citrix XenDesktop has never been simpler. Yes, this is still a potentially very large scale distributed architecture that solves a complicated problem, but the moving parts have been greatly simplified. One of the most important architectural shifts involves the way XenApp is integrated within a XenDesktop Infrastructure. Now the management infrastructures are combined and all that separates shared hosted sessions vs dedicated desktops are where the Virtual Delivery Agent (VDA) is installed. All “XenApp” really means now is that the VDA is installed on an RDSH host, physical or virtual. That’s it! Otherwise, Machine Creation Services (MCS) performance is getting closer to Provisioning Services (PVS) and catalogs/ delivery groups have never been easier to manage.

 

Support for Dell EqualLogic PS6210 series

Dell EqualLogic has begun shipping the new and improved PS6210 series which most notably provides the DWD Tier 1 iSCSI hybrid array: PS6210XS. Not only are the Base-T and SFP controller ports doubled but so is the performance! We have literally seen a 100% performance improvement on the PS6210XS hosting VDI desktops which will stretch your shared storage dollar and users per rack unit even further.

 

Dell Wyse Cloud Client updates

DWD E2E solutions provide everything required to design, implement and manage industry leading VDI infrastructures. This of course includes one of the most important aspects which is how the end user actually interfaces with the environment: the client. DWD for Citrix XenDesktop includes Citrix Ready clients to meet any organization need. ThinOS, Windows Embedded, Linux, dual/quad core, BYOD, HDMI, tablet and Chromebook.  

 

 

 

 

 

 

 

 

 

One of the most exciting new clients from Dell Wyse is the Cloud Connect. The Cloud Connect turns any HDMI-enabled TV or monitor into a thin client through which to access your VDI desktop. Portable and high performing!

 

High performance SAN-less blade offering

New in DWD is a high-performance SAN-less blade offering that leverages Citrix MCS. This very simple but high performance design makes use of a pair of 800GB SSDs in each blade to host the mgmt or compute functions. Gold images are stored on each compute blade with a corresponding non-persistent pool spun up on each blade by the Delivery Controller. This configuration is capable of supporting the maximum possible compute host density based on our standard CPU and RAM recommendations. HA is provided as an option for the mgmt layer through the introduction of shared Tier 2 and clustering with a second mgmt blade.

 

Support for LoginVSI 4

Login Consultants Login VSI is the industry standard VDI load generation tool to simulate actual workloads. Moving from version 3.7 to 4 introduces some changes in the load generated and consequently the densities we see on our VDI solution infrastructures. Mostly notably, version 4 reduces the amount of read/write IO generated but increases the CPU utilization. All of our test results have been updated using the new tool.

 

 

High IOPS persistent desktops using Atlantis ILIO

Partnering with Atlantis Computing, we have collaborated on a solution to deliver high IOPS for persistent desktops where disk is typically at a premium. ILIO is a software solution that fits seamlessly into the existing Local Tier 1 model for DWD that makes use of compute host RAM to store and execute desktop VMs. No server medium is faster than RAM and with ILIO’s deduplication ability, only a fraction of the storage that would otherwise be required is necessary. This solution fits easily with the highly reliable and economical 1Gb EqualLogic PS6100E that provides hosting to the mgmt VMs, user data, and persistent desktop data.

 

Citrix vGPU support for graphical acceleration

Fleshing out the DWD virtualized graphics offerings, we are proud to include the new Citrix vGPU technology which utilizes the NVIDIA Grid boards. For XenDesktop, we offer vDGA (pass-through) and vSGA (shared) graphics on vSphere and now vGPU on Citrix XenServer. vGPU enables a hybrid variety of graphic acceleration by sharing the on-board GPUs while also enabling OpenGL capabilities by running graphics drivers in the VMs themselves. This is done through vGPU profiles that are targeted to specific use cases and maximum Grid board capabilities. The higher the resources consumed with higher resolutions = fewer users per Grid board.

High level vGPU architecture:

 

Stay tuned for more exciting VDI products from Dell coming late this spring. Citrix Synergy is right around the corner. In the meantime please check out our RAs and thanks for stopping by!

We finally have the past several months of work published in our latest RAs. I posted the VRTX + XenDesktop RA earlier  which was part of this release but made it out the door first.

Reference Architecture for DVS Enterprise for Citrix XenDesktop 7: Link

Notable new features included in this release:

 

Intel Ivy Bridge CPU support for all servers (E5-2600 v2) with increased user densities

Intel Ivy Bridge CPUs enable greater performance capability in the existing 12G Dell PowerEdge server line. More cores and faster RAM clocks are now available to get more out of every dollar invested in your VDI deployment. Using Hyper-v 2012 with PVS on XenDesktop 7 we are now seeing user densities of up to 200 concurrent per compute host! It should be said that we tested with the new 1866MHz DIMMs and found no benefit to justify the cost increase over the 1600MHz DIMMs.

 

Dell PowerEdge M IO Aggregator added to extended SCL replacing M8024-K modules

The IO Aggregator modules are used in the A frabic of the M620 blade-based solutions for 10Gb connectivity (internal + uplink). They can be used to provide 20Gb of iSCSI bandwidth to each blade or can be sliced into virtual NICs for LAN traffic, using NPAR, for fiber channel solutions.

 

Update to Dell Compellent Tier 1 scaling and configuration (SCOS 6.3)

SCOS 6.3 brings with it some exciting performance enhancements to the Dell Compellent SC8000 controller architecture. We saw a 200% performance improvement over the legacy 6.2 code bringing the DVS recommended Compellent array to support upwards of 2000 users. Keep in mind that this is pure SAS, no SSD or fancy flash, and that’s not the top end for this array either. We’ll be pushing this array further in the months to come. This update adds 2 additional shelves to the existing 1000 user offering and is capable of booting them all on-demand in less than an hour.

 

Dell Wyse Cloud Client updates

Citrix Ready and certified for use with HDX to achieve the best end user experience possible.

 

Dell PowerEdge VRTX offering for ROBO: LINK

Dell’s award-winning and industry recognized consolidated infrastructure used to host up to 500 VDI users at a price that can’t be beat.

 

Shared graphics (vSGA) on NVIDIA Grid cards: LINK

We’ve expanded our graphic acceleration offering to include vSGA (shared mode) in addition to vDGA (pass-through mode) on VMware vSphere. vSGA offers a higher per compute host user density by virtualizing the GPU cores.

 

Microsoft Lync 2013 test results and sizing: LINK

Unified Communications in VDI can be tricky. Dell DVS has put Lync 2013 through its paces in the XenDesktop environment and demonstrates what can be expected from a sizing and performance perspective.

[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.