This webinar will cover the current state of MCS and PVS. We'll look at how MCS and PVS work differently on hypervisors like ESXi and Hyper-V. We will look at new target platforms such as Windows Server 2012 R2 to see if PVS or MCS behave differently. And lastly we will dive into the new VHDX-based PVS wC option and why you should be using it for all your workloads. The webinar will be presented by Nick Rintalan

1. PVS vs. MCS  PVS & MCS!
Nick Rintalan
Technical Deep Dive
Lead Architect, Americas Consulting, Citrix Consulting
August 5, 2014

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Agenda
Myth Busting
The New PVS wC Option
Detailed Performance Testing & Results
Key Takeaways
Q & A

3. Myth Busting!

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Myth #1 – PVS is Dead!
PVS is alive and well
Not only are we (now) enhancing the product and implementing new features
like RAM cache with overflow to disk, but it has a healthy roadmap
Why the Change of Heart?
• We realized PVS represents a HUGE competitive advantage versus VMW
• We realized our large PVS customers need a longer “runway”
• We actually had a key ASLR bug in our legacy wC modes we had to address

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Myth #2 – MCS Cannot Scale
Most people that say this don’t really know what they are talking about 
And the few that do might quote “1.6x IOPS compared to PVS”
The 1.6x number was taken WAY out off context a few years back (it took into
account boot and logon IOPS, too)
Reality: MCS generates about 1.2x IOPS compared to PVS in the steady-state
• 8% more writes and 13% more reads, to be exact
• We have a million technologies to handle those additional reads!
But performance (and IOPS) are only one aspect you need to consider when
deciding between PVS and MCS…

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Myth #3 – MCS (or Composer) is Simple on a Large Scale
MCS (or any technology utilizing linked clone’ish technology) still leaves a bit to
be desired from an operations and management perspective today
• Significant time required when updating a large number of VDIs (or rolling back)
• Controlled promotional model
• Support for things like vMotion
• Some scripting may be required to replicate parent disks efficiently, etc.
MCS is Simple/Easy
• I’d agree as long as it is somewhat small’ish (less than 1k VDIs or 5k XA users)
• But at real scale, MCS is arguably more complex than PVS
• How do you deploy MCS or Composer to thousands of desktops residing on hundreds of
LUNs, multiple datastores and instances of vCenter, for example?
• This is where PVS really shines today

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Myth #4 – PVS is Complex
Make no mistake, the insane scalability that PVS provides doesn’t come
absolutely “free”, so there is some truth to this statement 
BUT, have you noticed what we’ve done over the last few years to address this?
• vDisk Versioning
• Native TFTP Load Balancing via NS 10.1+
• We are big endorsers of virtualizing PVS (even on that vSphere thing)
• We have simplified sizing the wC file and we also endorse thin provisioning these days
- RAM Cache w/ overflow to disk (and thin provision the “overflow” disk = super easy)

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Myth #5 – PVS Can Cause Outages
So can humans! 
And if architected correctly, using a pod architecture, PVS cannot and should not
take down your entire environment
Make sure every layer is resilient and fault tolerant
• Don’t forget about Offline Database Support and SQL HA technologies (mirroring)
We still recommend multiple PVS farms with isolated SQL infrastructure for our
largest customers – not really for scalability or technical reasons, but to minimize
the failure domain

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Myth #6 – XenServer is dead and MCS only works with IntelliCache
Just like PVS, XenServer is also alive and well
• We just shifted our focus a bit
• Contrary to popular belief, we are still actively developing it
We are implementing hypervisor level RAM-based read caching in XS.next
• Think “IntelliCache 2.0” (no disks or SSDs required this time!)
• The new in-memory read caching feature and the old IC feature can even be combined!
Did you know that MCS already works and is supported with CSV Caching in
Hyper-V today?
Did you know that MCS also works with CBRC?
• We even have customers using it in production! (Just don’t ask for official support)

10. The new PVS wC Option
aka “The Death of IOPS”

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RAM Cache with Overflow to Disk – Details
First and foremost, this RAM Caching is NOT the same as the old PVS RAM
Cache feature
• This one uses non-paged pool memory and we no longer manage internal cache lists, etc. (let
Windows do it – it is pretty good at this stuff as it turns out!)
• Actually compared the old vs. new RAM caching and found about 5x improvement in
throughput
Pretty simple concept: leverage memory first, then gracefully spill over to disk
• VHDX-based as opposed to all other “legacy” wC modes, which are VHD-based
- vdiskdif.vhdx vs. .vdiskcache
• Requires PVS 7.1+ and Win7/2008R2+ targets
• Also supports TRIM operations (shrink/delete!)

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RAM Cache with Overflow to Disk – Details Con’t
The VHDX spec uses 2 MB chunks or block sizes, so that is how you’ll see the
wC grow (in 2 MB chunks)
The wC file will initially be larger than the legacy wC file, but over time, it will not
be significantly larger as data will “backfill” into those 2 MB reserved blocks
This new wC option has nothing to do with “intermediate buffering” – totally
replaces it
This new wC option is where we want all our customers to move ASAP, for not
only performance reasons but stability reasons (ASLR)

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Why it works so well with only a little RAM
A small amount of RAM will give a BIG boost!
All writes (mostly random 4K) first hit memory
They get realigned and put into 2 MB memory blocks in Non-Paged Pool
If they must flush to disk, they get written as 2 MB sequential VHDX blocks
• We convert all random 4K write IO into 2 MB sequential write IO
Since Non-Paged Pool and VHDX are used we support TRIM operations
• Non-Paged Pool memory can be reduced and the VHDX can shrink!!!!
• This is very different than all our old/legacy VHD-based wC options

14. Performance Results

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Our First Field Test (XA workloads w/ vSphere)
Used IOMETER to compare legacy wC options and new wC option
• #1 – “line test” (i.e. no PVS)
• #2 and #3 – new wC option
• #4 – legacy RAM cache option
• #5 – legacy disk cache option (which 90% of our customers use today!!!)

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Our Second Field Test (XD workloads w/ vSphere and Hyper-V)
Win7 on Hyper-V 2012 R2 with 256 MB buffer size (with bloated profile):
Win7 on vSphere 5.5 with 256 MB buffer size (with bloated profile):

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And Even More Testing from our Solutions Lab
LoginVSI 4.0
Variables
• Product version
• Hypervisor
• Image delivery
• Workload
• Policy
Hardware
• HP DL380p G8
• (2) Intel Xeon E5-2697
• 384 GB RAM
• (16) 300 GB 15,000 RPM spindles in RAID 10

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0
50
100
150
200
250
2008R2 2012R2 2012R2 2012R2 2012R2 2012R2 2008R2 2012R2 2012R2 2012R2 2012R2 2012R2
UX UX UX Scale UX UX UX UX UX Scale UX UX
Medium Light Medium Medium Medium Medium Medium Light Medium Medium Medium Medium
PVS (Disk) MCS MCS MCS PVS (Disk) PVS (RAM) PVS (Disk) MCS MCS MCS PVS (Disk) PVS (RAM)
Hyper-V Hyper-V Hyper-V Hyper-V Hyper-V Hyper-V vSphere vSphere vSphere vSphere vSphere vSphere
6.5 7.5 7.5 7.5 7.5 7.5 6.5 7.5 7.5 7.5 7.5 7.5
VSI Max
(XenApp 7.5 - LoginVSI 4)

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0
50
100
150
200
250
Hyper-V 2012R2 vSphere 5.5
MCS PVS (Disk) PVS (RAM with Overflow)
PVS vs MCS
Notable XenApp 7.5 Results
Imaging platform does
NOT impact single
server scalability

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0
10
20
30
40
50
60
70
80
90
Hyper-V 2012R2 vSphere 5.5
MCS PVS (Disk) PVS (RAM with Overflow)
PVS vs MCS
Notable XenDesktop 7.5 Results
Imaging platform does
NOT impact single
server scalability

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10
Hyper-V vSphere
MCS PVS (Disk) PVS (RAM with Overflow)
MCS vs PVS (Disk) vs PVS (RAM with Overflow)
Notable XenDesktop 7.5 Results
PVS (RAM with Overflow)
less than 0.1 IOPS with
512MB RAM Cache!!!
0.1 IOPS
per user

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0
0.1
0.2
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0.4
0.5
0.6
0.7
0.8
0.9
1
PVS (RAM with Overflow)
512MB 256MB
PVS (RAM with Overflow) 512 MB vs 256 MB
Notable XenDesktop 7.5 Results
• 512 MB RAM = .09 IOPS
• 256 MB RAM = .45 IOPS

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180
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12
23
34
45
56
67
78
89
100
111
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133
144
155
166
177
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540
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573
584
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617
628
639
IOPS
Total Host IOPS (100 users on host)
PhysicalDisk -- Disk Transfers/sec -- _Total
Peak IOPS
Notable XenApp 7.5 Results
Peak = 155 IOPS

24. Key Takeaways & Wrap-Up

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Key Takeaways
Performance/Scalability is just one element to weigh when deciding between
MCS and PVS
• Do NOT forget about manageability and operational readiness
• How PROVEN is the solution?
• How COMPLEX is the solution?
• Do you have the ABILITY & SKILLSET to manage the solution?
• Will it work at REAL SCALE with thousands of devices?
The new VHDX-based PVS 7.x write cache option is the best thing we have given
away for FREE since Secure Gateway (IMHO)
It doesn’t require a ton of extra memory/RAM – a small buffer will go a long way

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Key Takeaways – Con’t
For XD workloads, start with 256-512 MB buffer per VM
For XA workloads, start with 2-4 GB buffer per VM
If you are considering vSAN, buying SSDs or a niche storage array, STOP
immediately what you’re doing, test this feature and then have a beer to celebrate
We just put IOPS ON NOTICE!
• http://blogs.citrix.com/2014/07/22/citrix-puts-storage-on-notice/
• Now all you really have to worry about are the IOPS associated with things like the pagefile and
event logs

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WORK BETTER. LIVE BETTER.