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Atlantis Computing™ U.S. Headquarters 2570 El Camino Real, Suite 230
Mountain View, CA 94040
Phone: +1 (650) 917-9471
Email: [email protected]
Twitter: @AtlantisILIO
Atlantis Computing European Headquarters 3rd Floor Cutlers Court
115 Houndsditch
London EC3A 7BR
+44 (0) 203 405-2851
@AtlantisILIO www.atlantiscomputing.com
Citrix XenApp on VMware vSphere and Atlantis ILIO
Best Practices Guide
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1 EXECUTIVE SUMMARY ................................................................................................................................. 2
2 SOLUTION OVERVIEW .................................................................................................................................. 3
2.1 Citrix XenApp .............................................................................................................................................. 3
2.2 Atlantis ILIO for Citrix XenApp ............................................................................................................. 4
2.2.1 Absorb Storage Sizing Mistakes – Lowers Deployment Risks ........................................................... 4
2.2.2 Atlantis ILIO for XenApp Benefits ................................................................................................................. 5
2.2.3 Atlantis ILIO In-Memory Storage Optimization Technology ............................................................. 5
3 ATLANTIS ILIO FOR CITRIX XENAPP SOLUTION ARCHITECTURE ................................................ 6
4 ATLANTIS ILIO FOR XENAPP DESIGN CONSIDERATIONS ................................................................ 7
4.1 XenApp Deployment Method................................................................................................................. 7
4.2 Placement of the PVS Write Cache ....................................................................................................... 7
4.3 Storage options for Citrix XenApp ....................................................................................................... 7
4.4 Atlantis ILIO for XenApp Deployment Method................................................................................ 8 4.4.2 Capacity requirements for XenApp .............................................................................................................. 9
4.4.3 IOPS requirements for XenApp .................................................................................................................... 10
4.4.4 Recommendation ............................................................................................................................................... 10
5 ATLANTIS ILIO FOR XENAPP DEPLOYMENT CONSIDERATIONS ................................................ 11
5.1 Atlantis ILIO Configuration ................................................................................................................. 11
5.1.1 Atlantis ILIO Processor Allocation .............................................................................................................. 11
5.1.2 CPU Hyperthreading Configuration ........................................................................................................... 11
5.1.3 Memory Allocation and Reservation ......................................................................................................... 11
5.1.4 Networking Configuration ............................................................................................................................. 12
6 ATLANTIS ILIO FOR XENAPP MANAGEMENT CONSIDERATIONS ............................................... 14
6.1 Snap Clone management ...................................................................................................................... 14
7 CONCLUSION ................................................................................................................................................. 15
7.1 Additional resources ............................................................................................................................. 15
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1 Executive Summary
Many businesses are in the process of virtualizing Citrix
XenApp and migrating to XenApp 6.5 on Windows Server
2008 R2/2012. Virtualizing XenApp introduces new data
center infrastructure and performance challenges typically
associated to the use and sizing of the shared storage
needed for the implementation. Failing to properly address
those storage and networking bottlenecks almost always
results in significant cost overruns and project delays.
This guide describes a scalable and high-performance
desktop virtualization solution consisting of Citrix XenApp
and Atlantis ILIO for XenApp™, which is the only solution
that makes it possible to deploy virtualized XenApp with no
shared storage or SSDs – using Atlantis ILIO In-Memory
Storage™ technology that turns server RAM into storage to
run virtualized XenApp instances.
The guide contains a set of best practices for the deployment of Citrix XenApp and Atlantis ILIO™ for
XenApp.
Solution Benefits
Absorb PVS Write Cache growth – avoid costly re-architecting and unexpected storage CAPEX costs overruns due to application/dataset changes and XenApp expansion
Automated and Simpler Deployment – Fully automated multi-rack deployment to deploy faster with less people and risks – push button automation
Cuts CAPEX and OPEX costs – No shared storage or SSDs. Uses server RAM as primary storage for virtualized XenApp instances
Amazing User Experience, Provisioning and Boot Times – accelerates logons, application startup and performance
Increases Density – increase density by up to 20% while delivering a better user experience
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2 Solution Overview
Atlantis ILIO for XenApp™ software simplifies virtualized Citrix XenApp architectures, automates
deployments and boosts desktop and application performance. Atlantis ILIO increases the number of
users per server and uses server RAM as primary storage to scale out a virtualized XenApp deployment
with no physical storage or SSDs. Automation lowers project risks by deploying faster with less people
and without human errors and simplifies large scale desktop virtualization management.
2.1 Citrix XenApp
Citrix XenApp empowers users with on-demand self-service to enterprise applications. Used by more
than 100 million people worldwide, XenApp is an application delivery solution that enables any
Windows® application to be virtualized, centralized and managed in the datacenter and instantly
delivered as a service to users anywhere on any device. Virtual application delivery with XenApp enables
organizations to improve application management by:
Centralizing applications in the datacenter to reduce complexity and lower the cost of desktop management by up to 50 percent
Controlling and encrypting access to data and applications to improve security
Delivering applications instantly to users anywhere on any device
Simplifying and automating the process of delivering or updating applications, enabling IT to focus on strategic initiatives
Citrix XenApp is one of the deployment options of Citrix XenDesktop (Citrix Terminology: Hosted Shared)
that allows users to connect to their enterprise applications or published desktops from a variety of
client devices such as thin clients, PCs, and iOS devices supported by the Citrix Receiver. Citrix XenApp
connects multiple users to a shared Windows Server 2003/2008R2 server that hosts one or more
applications on a central server and allows users to access their applications remotely.
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2.2 Atlantis ILIO for Citrix XenApp
Atlantis ILIO for Citrix XenApp is a software optimization solution that enables the virtualization of Citrix
XenApp with no physical storage, while addressing write cache sizing issues, automating deployments
and boosting performance. Atlantis ILIO for Citrix XenApp uses ILIO In-Memory Storage™ technology
that turns Server RAM into storage to run virtualized Citrix XenApp servers.
2.2.1 Absorb Storage Sizing Mistakes – Lowers Deployment Risks
Citrix XenApp is most commonly deployed using Citrix Provisioning Server (PVS), which requires storage
for a write-cache that can vary in size from 1GB to more than 20GB depending on the number of users,
workloads and applications. More than 50% of XenApp deployments are configured with a Write Cache
size that is bigger than 10GB per XenApp virtual machine1, which means that the storage capacity that is
required for a XenApp deployment can quickly grow to large storage requirements.
When using SAN/NAS or SSDs, write-cache under-sizing, even by a small percentage, can lead to very
large incremental project costs and delays. These changes might be necessary due changes business
requirements, resulting in application changes or data set increases, or incurred because the XenApp
deployment is growing which requires more XenApp virtual machines to be deployed. Atlantis ILIO
addresses the risks introduced due to such changes by absorbing write cache growth through the
Atlantis ILIO storage optimization solution.
An often under-estimated factor while designing and implementing virtualized XenApp is the number of
IOPS per XenApp user that the shared storage needs to be able to provide. Citrix estimates that a heavy
XenApp user generates about 8 IOPS on average, which is lighter than a typical VDI user as the IO
operations generated by the OS are shared across multiple users but as XenApp deployments typically
are much larger than VDI deployment, the total number of IOPS required to provide all end users with a
good user experience is significant. Please refer to section 0 for an example of the calculation of storage
requirements for a 1,000 user XenApp deployment on a RAID-5 storage array.
Furthermore, Atlantis ILIO for XenApp leverages Server RAM as In-Memory storage for the virtualized
XenApp instances, eliminating any storage and networking bottlenecks
1 http://blogs.citrix.com/2011/10/31/pvs-write-cache-sizing-considerations-%E2%80%93-follow-up/6-6/
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2.2.2 Atlantis ILIO for XenApp Benefits
Reduces Risk PVS Write Cache Sizing – addresses errors that lead to large incremental CAPEX expenditure
Automated Deployment – Eliminates human errors and speeds deployments by automating the installation and configuration of the storage infrastructure
Simpler Deployment – no risk of storage or network bottlenecks
Cuts Costs and Complexity Storage – No shared storage or SSDs for XenApp – uses In Memory Storage™ technology
Network – No storage traffic for the PVS Write Cache simplifies network design
Session Density – increase in the number of users per XenApp server
Increases Performance Applications – In-Memory storage accelerates response times
Provisioning – faster provisioning Boot time – faster boot times
2.2.3 Atlantis ILIO In-Memory Storage Optimization Technology
Analyzing & Processing IO Traffic – Atlantis ILIO performs context-aware processing in real-time at the file system and block levels to significantly reduce the amount of traffic sent to storage.
Inline De-duplication – Atlantis ILIO performs inline de-duplication in real-time on-the-wire, eliminating up to 95%* of the blocks before reaching storage.
Compression – Atlantis ILIO compresses the optimized blocks before writing them to memory.
IO Blender Fix – Atlantis ILIO coalesces small random blocks generated by the Windows operating systems and hypervisors into larger blocks of sequential IO, greatly improving efficiency.
Fast Clone – Clones full XenApp VMs in as little as 5 seconds without network or storage traffic.
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3 Atlantis ILIO for Citrix XenApp Solution Architecture
The Atlantis ILIO software virtual machine is automatically deployed on each physical host, creating a
highly optimized datastore using only server RAM as storage for all XenApp virtual machines. With Citrix
Provisioning Server (PVS), the write-cache is placed on the Atlantis ILIO data store to accelerate
performance, provide virtually unlimited IO, and simplify the deployment of Citrix XenApp.
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4 Atlantis ILIO for XenApp Design Considerations
4.1 XenApp Deployment Method
Atlantis ILIO for XenApp supports the two deployment methods for virtualized XenApp:
Stand-alone XenApp Virtual Machines
Provisioning Services for single image management
The storage performance profile of either deployment method is very similar - a large number of 4k
random IO blocks with a high write I/O ratio (typically 80 or 90% of the XenApp IO/O). The storage
optimization results of Atlantis ILIO for XenApp for both profiles are very similar , with typical
optimization ratios of about 90% for IOPS reduction as well as space utilization reduction. In addition,
the Atlantis ILIO NFS datastore leverages Atlantis ILIO In-Memory Storage to access Server RAM, and
provides virtually unlimited IOPS to the XenApp virtual machines.
4.2 Placement of the PVS Write Cache
Administrators typically place the PVS Write Cache for their XenApp instances on shared SAN/NAS
storage. This enables advanced management operations such HA and DRS for the XenApp instances.
With a typical density of 4-12 XenApp virtual servers per physical host, the capacity and performance
requirements add up quickly as you scale the number of XenApp users2.
4.3 Storage options for Citrix XenApp
The above graph3 highlights the fact that most organizations use central storage (NAS or NAS) for their
XenApp deployments. SSD Storage Arrays, used by approximately 10% of the organizations, are able to
2 http://blogs.citrix.com/2011/10/31/pvs-write-cache-sizing-considerations-–-follow-up 3 Project VRC - State of the VDI and SBC Union 2013 v1.0 - http://www.projectvrc.com/
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deliver the storage performance in terms of low latency and more IOPS per desktop than disk-based
SAN/NAS but have a cost per GB of $25-$35 that makes XenApp deployments costly in terms of CAPEX.
In addition, purchasing, installing, maintaining and repairing a completely new storage system that is
unproven and different from your existing storage infrastructure adds OPEX cost and operational risk.
Local SSDs on the other hand have a high cost per GB and limited storage capacity which both increases
cost and limits server options. The write-heavy and randomized workload of XenApp can cause lower
cost MLC SSDs to fail within the deployment duration of your XenApp farm. While more expensive SLC
SSDs last longer, their lifespan is still limited and they may fail within the typical lifespan of 3-5 yearsof a
XenApp deployment. When local SSDs fail, the drives must be replaced manually and the server re-
configured to bring it back online. The CAPEX cost of regularly purchasing additional disks and the
operational cost of supporting the local SSDs can be much more expensive than the original purchase
price of the SSDs.
4.4 Atlantis ILIO for XenApp Deployment Method
Atlantis ILIO for XenApp should be installed following the instructions in the product Administration
Guide. This will result in a deployment with one Atlantis ILIO virtual machine per hypervisor host that is
used to run multiple XenApp virtual machines.
Atlantis ILIO for XenApp can be deployed in one of the two following deployment types:
1. Atlantis ILIO using In-Memory Storage™
2. Atlantis ILIO using disk-backed storage
The preferred deployment option with In-Memory Storage, all XenApp virtual machine images or PVS
Write Caches are stored on In-Memory storage, providing ultra-fast access to the virtual machine
storage and eliminating any external storage traffic on the SAN or network.
Using disk-backed storage, Atlantis ILIO optimizes the IO traffic generated by the XenApp virtual
machines before it actually hits the physical storage. By optimizing the traffic using the Atlantis ILIO, you
typically reduce the amount of IO by up to 90% in terms of IOPS and up to 95% for capacity.
We recommend using the In-Memory Storage deployment type for your XenApp deployment, since
practically all XenApp deployments are stateless and don’t need to store virtual machine images on
persistent storage. This deployment type eliminates the need for any storage networking or the
presence of physical storage.
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4.4.2 Capacity requirements for XenApp
A field poll executed by Citrix4 shows that the most common Write Cache size is 16-20GB per XenApp
Virtual Machine. At a typical density of 8 XenApp virtual machines per physical host, you need at least
160GB of storage for the PVS Write Caches.
Some organizations decide to use fast local hard disks such as SSDs as the location of the PVS Write
Caches, but this choice inherently exposes your organization to a few serious risks:
If your organization is in a situation where the initial sizing of the PVS Write Cache was
determined incorrectly and needs to increase the size of the Write Cache, you will have to
purchase expensive SSDs with an increased capacity to replace existing drives
The storage profile of PVS Write Cache IO workload is very write-intensive. SSDs with an
average P/E ratio5 will exhaust the available write cycles on the SSD over the average lifespan of
a PVS deployment, causing your organization to incur downtime, CAPEX and OPEX costs to
replace the SSDs
With Atlantis ILIO for XenApp, your organization
leverages server memory and Atlantis In-Memory
Storage technology, providing ultra-fast primary
storage to run the XenApp virtual machines. With
the Atlantis ILIO storage optimizations, the PVS
Write Cache size is reduced significantly so you can
either oversize your PVS Write Caches, or you can
grow your PVS Write Caches at a later point in your
XenApp deployment life cycle without any additional
CAPEX investments.
4 Sources: Citrix Blog http://blogs.citrix.com/2011/10/31/pvs-write-cache-sizing-considerations-–-follow-up/ http://blogs.citrix.com/2013/01/07/whats-the-optimal-xenapp-6-5-vm-configuration/ 5 http://en.wikipedia.org/wiki/Flash_memory#Memory_wear
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4.4.3 IOPS requirements for XenApp
Citrix guidelines estimate the average IOPS requirement between 2
and 8 IOPS per virtual desktop user (ranging for a light to a heavy
XenApp user)6. As the IO workload generated by Citrix XenApp has a
ratio of about 80-90% writes and 10-20% reads, the IO performance
requirements for used storage need to take the write penalty into
effect to effectively determine the storage performance of your
shared SAN / NAS storage required to deliver the required IOPS.
Undersizing the shared SAN / NAS storage will have direct effect on
the application performance and user experience.
RAID IO
Penalty Net Read IOPS for a 15K disk
Net Write IOPS for a 15K disk
Net Read IOPS for a 10K disk
Net Write IOPS for a 10K disk
RAID-0 0 160 160 120 120
RAID-1 2 160 80 120 60
RAID-5 4 160 45 120 35
RAID-6 6 160 30 120 20
RAID-DP 2 160 80 120 60
From ‘How to Implement Storage for Virtual Desktop Deployments’, by Gartner, Inc (G00245654), and Ruben Spruijt, PQR
The calculations for the IO performance requirements for a 1000 user virtualized XenApp deployment
with a mix of users (40% light, 40% medium and 20% heavy) on a SAN with RAID 5 configuration are as
follows:
Total frontend IOPS = (400 * 2) + (400 * 4) + (200 * 8) = 4,000 IOPS
SAN Read IOPS = 20% * 4,000 = 800 IOPS
SAN Write IOPS = 80% * 4,000 * 4 (RAID-5 write penalty) = 12,800 IOPS
Total SAN IOPS = 800 + 12,800 = 13,600 IOPS (or 13.6 backend IOPS per user)
At 160 IOPS per 15K SAS disk, you would need 85 SAN/NAS disks for these 1000 users.
4.4.4 Recommendation
Because Atlantis ILIO for XenApp uses In-Memory Storage technology to turn server RAM into a NFS
datastore, we recommend storing the full XenApp images or the PVS Write Caches on the Atlantis ILIO
datastore, removing the need for expensive local SSD storage or complex, shared SAN/NAS storage.
6 http://blogs.citrix.com/2013/01/07/whats-the-optimal-xenapp-6-5-vm-configuration/
PV
Source: Atlantis Computing Survey – March 2012
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5 Atlantis ILIO for XenApp Deployment Considerations
This section describes best practices for installation and configuration of Atlantis ILIO virtual machines.
5.1 Atlantis ILIO Configuration
The following sections describe Atlantis ILIO processor, memory, networking, and storage configuration.
5.1.1 Atlantis ILIO Processor Allocation
Setting the CPU Reservation value assures that the Atlantis ILIO virtual machine receives sufficient
processing cycles when there are other virtual machines on the same hypervisor as Atlantis ILIO (for
example, Virtual Desktops or Virtual Servers). This is important as Atlantis ILIO is offloading I/O from
shared storage into compute resources within the ILIO VM. This reservation allows us to protect
resources for Atlantis ILIO and guarantee user performance.
It is required that a minimum of one vCPU (with a minimum clock speed of 2000 MHz) be allocated to
the Atlantis ILIO virtual machine. Additional vCPUs may be necessary for some deployments depending
on the number of VMs and workload. An additional vCPU may be needed when compression is enabled
such as for an Atlantis Diskless VDI deployment. In general, allocating two vCPUs with one vCPU
reserved is recommended.
5.1.2 CPU Hyperthreading Configuration
Hyperthreading allows a single physical processor core to function as two logical processors. Although
the using Hyperthreading does not double the performance vs using the physical processor core as one
logical processor, there is a performance advantage. Atlantis ILIO can take advantage of Hyperthreading
and Hyperthreading should always be enabled.
5.1.3 Memory Allocation and Reservation
The Atlantis ILIO VM memory requirement is dependent on the type of the deployment (In-Memory
Storage or disk-backed), the number of virtual XenApp Server, the type of workload and the size of the
XenApp Virtual Machine image or the PVS Write Cache.
Atlantis ILIO RAMDISK and Memory Size Calculation (In-Memory Storage)
This section describes the calculation for the RAM disk size for hosting the Virtual XenApp Servers. The
‘image size’ in the formula can either refer to the in-use size of the XenApp virtual machine base image
(check the ‘Used Space’ in your hypervisor management tool), or the full size of the PVS write cache.
Formula
RAMDISK Size = {image size + (image size
* No. of XenApp Server VMs to be deployed
* (1 - 80%) disk usage offload)}
Example
If the write-cache size is assumed to be 10 GB and the total number of XenApp Server
VMs is 4, then the size of virtual disk will be:
RAMDISK Size = {10 GB + (10 GB * 4 * .2)} = 18 GB
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The ILIO memory calculation depends on the size of the RAM disk calculated above.
Formula
Memory Size = { (6 GB) OS memory
+ (RAMDISK size * 3%) metadata memory
+ RAMDISK size}
Example
If the size of the RAMDISK size is 18 GB then the memory size will be:
Memory Size = {6 GB + (18 GB * .03) + 18 GB} = 24.54 GB minimum
Note that after specifying the Atlantis ILIO VM memory size, the memory specified must be reserved. If
the memory is not reserved, a swap file the size of the memory allocated will be created on the
datastore where Atlantis ILIO is deployed.
5.1.4 Networking Configuration
Best practices for Atlantis ILIO Networking configuration falls into the following categories:
Selecting the correct networking driver.
Configuring hypervisor virtual switches.
Attaching hypervisor virtual switches to physical networking adapters.
Provide virtual networks for Virtual Desktops, Atlantis ILIO Center, Back-end disks, and
hypervisor management function – such as vSphere and vMotion.
At a high level, the best practices help to:
Maximize networking performance.
Isolate the networking traffic from the Atlantis ILIO export of NFS and iSCSI datastores to the
hypervisor from other network traffic. This networking traffic does not need to go to an external
network.
Provide connectivity between the various XenApp functions.
Networking Drivers
Atlantis ILIO versions 3.2 and later use the VMXNET 3 driver, the next generation of a paravirtualized NIC
designed for performance.
Networking Switches
Separate virtual network switches need to be configured to isolate networking traffic from the Atlantis
ILIO export of NFS datastores to the hypervisor from other network traffic. Once two virtual switches are
created, then virtual network ports and connections to physical NICs can be added.
Session Host
In the screen capture below, two switches have been configured: vSwitch0 and vSwitch1.
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vSwitch0 has three ports and connects to one Physical Adapter. The VMkernel port at the top is used for
hypervisor access to NFS datastores and for vSphere function such as vMotion. The VM Network port is
used by Virtual Desktops and Atlantis ILIO to access networking. Atlantis ILIO virtual network adapter
ETH0 is typically connected to this port. The Management Network port is used by Atlantis ILIO Center
to access Atlantis ILIO VMs for management function.
vSwitch1 has two ports and connects to one Physical Adapter. Atlantis ILIO virtual network adapter ETH1
is typically connected to this port. The ILIO-VMkernel port is used for hypervisor access to the Atlantis
ILIO NFS datastore. Atlantis ILIO will use this port to export a NFS datastore. The ILIO-NFS port is used
for virtual network access by Atlantis ILIO.
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6 Atlantis ILIO for XenApp Management Considerations
6.1 Snap Clone management
When running Atlantis ILIO for XenApp with the In-Memory Storage configuration, you can make use of
the Snap Clone functionality to persist a snapshot of the In-Memory datastore to persistent storage. This
snapshot automatically is restored after a system reboot to present a clean starting state to the XenApp
broker.
The Snap Clone functionality protects your deployment running only in volatile memory from
unexpected system crashes or power outages by storing the base state of the XenApp virtual machines
to persistent storage.
The formula to size the storage required for the SnapClone storage is twice the size of the RAMdisk:
Formula
Snap Clone Disk Size = { RAMDISK size * 2 }
Example
If the size of the RAMDISK size is 18 GB then the memory size will be:
Snap Clone Disk Size= { 18 GB * 2 } = 36 GB minimum
The Snap Clone needs to be updated whenever you make a provisioning change to XenApp instances on
a physical host, for instance when you provision a new XenApp instance or remove a XenApp instance. It
is recommended to create the Snap Clone as soon as possible after making the provisioning change,
while the XenApp virtual machines are in the powered off state. The recommendation is to thin-
provision the storage for the Snap Clones to minimize the amount of storage necessary, and to use the
lowest tier of storage available, as performance of the Snap Clone creation and restoration is not in the
critical path of the user experience.
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7 Conclusion
The proven solution of Citrix XenApp and Atlantis ILIO for XenApp optimizes Citrix Hosted Shared
deployments to simplify the architecture and deployment, to increase storage efficiency to support
more users, and to leverage Server RAM to deploy XenApp desktops and applications with no storage or
SSDs.
Typical deployment risks, such as undersizing your PVS Write Cache Size or exhausting the SSD lifespan
are addressed by the Atlantis ILIO In-Memory storage optimizations and using Server RAM as primary
storage. Manual installation and configuration errors and shortage of qualified personnel are tackled by
fully automated multi-rack deployment. In addition, large scale Disaster Recovery is possible to provide
failover capabilities across datacenters.
By removing the need for any shared SAN/NAS storage, you can any eliminate storage network
bottlenecks, increase session density, and you can provide an amazing user experience, including near-
instant application startup and fast session logons.
If you are interested in deploying dedicated virtual desktops, Atlantis ILIO Persistent VDI enables Citrix
XenDesktop and VMware View customers to run virtual desktops In-Memory using RAM as primary
storage, making persistent virtual desktops cheaper and faster than physical PCs. For more information
on Atlantis ILIO Persistent VDI, please visit http://www.atlantiscomputing.com/products/persistent-vdi
7.1 Additional resources
Project VRC – State of the VDI and SBC Union 2013 v1.0
Atlantis ILIO for XenApp Solution Brief
Citrix Ready Webinar - Virtualizing Citrix XenApp with No Storage or SSDs
US Army Case Study
Atlantis ILIO for XenApp Administration Guide (Customer Portal Login required)