The document discusses Citrix's virtual desktop framework, focusing on standard model architecture, provisioning techniques like Machine Creation Services (MCS) and Provisioning Services (PVS), and integration with various hypervisors including Nutanix Acropolis. It explains the operational differences between MCS and PVS and highlights central image management benefits for admins through features such as pooled and dedicated VMs. Additionally, it outlines the interaction between Citrix Studio, vCenter, and other hypervisors for efficient virtual desktop management.

1. 1

2. Who am I, who’s in my team, what are my resposibilities, talk about reference
architectures and so on.
2

3. Sports foto courtesy of Alfred Cop.
3

4. 4

5. Our starting point for today is the standard model Citrix uses to describe a virtual
desktop.
In this model , several layers and involved in handling the provisioning of the virtual
desktops.
The Desktop Layer describes the actual golden image, containing or running the apps
the user is going to use.
A best practice is to make this image as lean and mean as you can, before rolling it
out, to increase scalability and user density on the system.
The Control and Access layer contains the management tools we use to actually
perform the provisioning operations. Studio is the main interface from which we
control machine creation and assignment of users to these desktops, in combination
with other consoles like the PVS management console if we chose to use that as our
main provisioning tool.
The hypervisor in this model can be pretty much anything we would like. New kid on
the block is the Nutanix Acropolis Hypervisor, or AHV.
Finally at the bottom we find the compute and storage layer, which can be designed
and built in many ways, but not every combination of hardware and storage is
suitable for high scale virtual desktop environments.
5

6. A little history tour.
Automated provisioning has not always been a part of the portfolio. A long long time
ago , physicial deployments of XenApp ruled the world, leveraging the IMA
architecture.
The acquisition of Ardence, in 2006, brought a tool to the Citrix world that solved a
big problem for XenApp customers. No longer did they need to manually or semi-
automatically deploy physical installation of Windows servers and scripted installs of
XenApp, but servers could be ran from a single image. Later , when VDI was starting
to become a big new thing , Citrix redesigned the IMA architecture to allow for larger
scale of environments, which is now called the Flexcast Management Architecture.
This architecture allowed different types of desktop and apps delivery to be mixed
and managed from a single console. Big part of FMA was the introduction of a new
provisioning technique called Machine Creation Services.
First iteration of this was focused on VDI, and later Citrix brought XenApp over to the
FMA architecture as well.
6

7. Finally we now also bring the Nutanix Acropolis Hypervisor into the FMA supported
hypervisors. This means that AHV is now fully supported to not only run VM’s, but
also leverage MCS and PVS as provisioning techniques.
7

8. If we compare PVS and MCS on a high level there are 5 comparisions we can make.
First of all the platform: PVS works for both virtual and physical workloads. MCS only
supports a hypervisor based deployment.
Delivery of the master image will go over the network (streamed) , while MCS
leverages storage as it’s main delivery.
The source format used with PVS is a VHDX file of the master VM, which means a
conversion has to take place first. MCS leverages hypervisor based snapshots.
The storage layer that’s beeing used to store the writes is local disk focused in case of
PVS, while with MCS it leverages a datastore approach. These datastores can however
be locally attached.
Finally the infrastructure needed; PVS is made up of a separate architecture of one or
more PVS servers, and might need a separate network for streaming. MCS is fully
integrated into the XenDesktop Controllers.
8

9. Depending on your needs, you can choose between MCS and PVS.
MCS offers three modes, but they are all for virtual desktops only.
Pooled: set of non-persistent VM’s, all sharing the same master image, shared across
multiple users.
Pooled with PVS: set of non-persistent VM’s shared across multiple users, but with a
Personal vDisk attached.
Dedicated: Set of persistent VM’s spun of from a master image.
9

10. Pooled VM’s can be random (each time you get a new pristine VM, but it can be a
different one than you had previously), or Static which means you log into the same
named VM each time. It will still be cleaned on restart.
PVS based desktops only have one mode, which is assigned on first use, and from
that point on you will log into the same desktop each time, because it also
personalises the PVD which is fixed to the VM.
Dedicated VM’s can be pre-assigned or set to first use, but will in essence require
“normal” pc management in terms of updates, patches and software distribution,
since it will be a persistent VM after it’s deployment. Once you update the master
image, only new desktops spun off the master will run the newer version of the
master.
PVS allows you to stream desktops to either physical or virtual machines. The most
used mode of PVS is standard image mode, which means non-persistent. Persistent
image mode is mostly used to update the master.
10

11. Image from Pixabay.com
https://pixabay.com/en/vehicle-chrome-technology-193213/
11

12. Machine Creation Services mechanics:
MCS is fully integrated into Citrix Studio and does not require a separate installer or
configuration. It’s there on each XenDesktop Controller.
MCS itself is a VM creation framework that can be learned to understand different
hypervisors. No code is actually placed on the hypervisor.
The method used to provision VMs and link disks to it, differs per hypervisor, but MCS
fully controlls the creation of the VM’s and fires of the commands to the hypervisor’s
management platform or API’s.
12

13. (Image obtained and edited from http://knowyourmeme.com/memes/philosoraptor)
So you could say the XenDesktop controllers actually speak multiple languages.
First of all it understands how to speak to Vmware ESX, and it will do so by talking to
vCenter.
Hyper-V will be contacted through SCVMM, XenServer is beeing addressed through
XAPI.
Finally, Nutanix AHV is accessed through the Nutanix AHV plugin, which is in itself
beeing accessed through the Provisioning SDK
13

14. MCS itself runs as 2 services on every XenDesktop Controller.
First we have the Citrix Machine Creation Service, which interfaces with the chosen
hypervisor.
The Citrix AD identity service talks with Active Directory and manages the domain
accounts and domain memberships of the VMs.
On the virtual desktops the Virtual Desktop Agent also contains a service, which is the
Machine Identity Service.
This services manages the VM uniqueness.
14

15. MCS will enable central image management for the admin.
In a pooled static scenario it works as follows:
First of all you create your Golden Master VM, install your apps and the Citrix
XenDesktop VDA.
With this Golden Master, you create a Machine Catalog.
When you run through the wizard in Studio, you will be asked which VM and which
snapshot to use (it will create a snap if none is present).
This snapshot is flattened and copied to each configured datastore (in the host
connection details).
When the image has been copied, a preparation procedure is started to create the
identity disk. This VM is then discarded and the main catalog VM’s are beeing cloned.
When cloned, each VM is attached to the master image (read only) and to a diff disk
(writable) and an ID disk (read only). The diff disk can grow as writes happen, but the
ID disk is a fixed 16 MB size.
15

16. MCS will enable central image management for the admin.
In a pooled static scenario it works as follows:
First of all you create your Golden Master VM, install your apps and the Citrix
XenDesktop VDA.
With this Golden Master, you create a Machine Catalog.
When you run through the wizard in Studio, you will be asked which VM and which
snapshot to use (it will create a snap if none is present).
This snapshot is flattened and copied to each configured datastore (in the host
connection details).
When the image has been copied, a preparation procedure is started to create the
identity disk. This VM is then discarded and the main catalog VM’s are beeing cloned.
When cloned, each VM is attached to the master image (read only) and to a diff disk
(writable) and an ID disk (read only). The diff disk can grow as writes happen, but the
ID disk is a fixed 16 MB size.
16

17. MCS will enable central image management for the admin.
In a pooled static scenario it works as follows:
First of all you create your Golden Master VM, install your apps and the Citrix
XenDesktop VDA.
With this Golden Master, you create a Machine Catalog.
When you run through the wizard in Studio, you will be asked which VM and which
snapshot to use (it will create a snap if none is present).
This snapshot is flattened and copied to each configured datastore (in the host
connection details).
When the image has been copied, a preparation procedure is started to create the
identity disk. This VM is then discarded and the main catalog VM’s are beeing cloned.
When cloned, each VM is attached to the master image (read only) and to a diff disk
(writable) and an ID disk (read only). The diff disk can grow as writes happen, but the
ID disk is a fixed 16 MB size.
17

18. MCS will enable central image management for the admin.
In a pooled static scenario it works as follows:
First of all you create your Golden Master VM, install your apps and the Citrix
XenDesktop VDA.
With this Golden Master, you create a Machine Catalog.
When you run through the wizard in Studio, you will be asked which VM and which
snapshot to use (it will create a snap if none is present).
This snapshot is flattened and copied to each configured datastore (in the host
connection details).
When the image has been copied, a preparation procedure is started to create the
identity disk. This VM is then discarded and the main catalog VM’s are beeing cloned.
When cloned, each VM is attached to the master image (read only) and to a diff disk
(writable) and an ID disk (read only). The diff disk can grow as writes happen, but the
ID disk is a fixed 16 MB size.
18

19. MCS will enable central image management for the admin.
In a pooled static scenario it works as follows:
First of all you create your Golden Master VM, install your apps and the Citrix
XenDesktop VDA.
With this Golden Master, you create a Machine Catalog.
When you run through the wizard in Studio, you will be asked which VM and which
snapshot to use (it will create a snap if none is present).
This snapshot is flattened and copied to each configured datastore (in the host
connection details).
When the image has been copied, a preparation procedure is started to create the
identity disk. This VM is then discarded and the main catalog VM’s are beeing cloned.
When cloned, each VM is attached to the master image (read only) and to a diff disk
(writable) and an ID disk (read only). The diff disk can grow as writes happen, but the
ID disk is a fixed 16 MB size.
19

20. If you want to do updates, all it takes it to perform the update is to boot up the
master, perform the change and choose the “Update Catalog” function in Studio.
It then creates a snapshot and copies a new flattened image to the datastore(s).
Depending on the options you choose you can have all VM’s pointed to the new
image right away, or do it in a rolling fashion. You can also rollback later if you want.
When you roll out a new image, on restart of the VM’s, they are pointed to the new
version, and the diffs are cleared.
20

21. If you want to do updates, all it takes it to perform the update is to boot up the
master, perform the change and choose the “Update Catalog” function in Studio.
It then creates a snapshot and copies a new flattened image to the datastore(s).
Depending on the options you choose you can have all VM’s pointed to the new
image right away, or do it in a rolling fashion. You can also rollback later if you want.
When you roll out a new image, on restart of the VM’s, they are pointed to the new
version, and the diffs are cleared.
21

22. If you want to do updates, all it takes it to perform the update is to boot up the
master, perform the change and choose the “Update Catalog” function in Studio.
It then creates a snapshot and copies a new flattened image to the datastore(s).
Depending on the options you choose you can have all VM’s pointed to the new
image right away, or do it in a rolling fashion. You can also rollback later if you want.
When you roll out a new image, on restart of the VM’s, they are pointed to the new
version, and the diffs are cleared.
22

23. If you want to do updates, all it takes it to perform the update is to boot up the
master, perform the change and choose the “Update Catalog” function in Studio.
It then creates a snapshot and copies a new flattened image to the datastore(s).
Depending on the options you choose you can have all VM’s pointed to the new
image right away, or do it in a rolling fashion. You can also rollback later if you want.
When you roll out a new image, on restart of the VM’s, they are pointed to the new
version, and the diffs are cleared.
23

24. Now lets take a look at how Citrix Studio connects with all the different hypervisors.
Citrix Studio normally resides on a XenDesktop controller en interfaces with the
different services running on the host.
These services take care of the brokering, manage the hosting connection and do the
MCS related tasks we mentioned earlier.
Studio is not the only way to interface with the core of XenDesktop, Powershell
CMDlets are also available directly.
When using Vmware, Citrix Studio talks to vCenter. vCenter therefore needs to be
made highly available if you want to make sure
You can always manage your environment or have Studio manage the VMs, maintain
the idle pools etc.
Should vCenter go down, you will not lose the current sessions, and any VMs that
have already registered themselves with the broker are still available for login.
vCenter in turn does the actual power on/power off of the VMs and the tasks related
to provisioning.
To get the most your storage and use the benefits on thin provisioning, Citrix
recommends using NFS datastores connected to the hypevisor hosts.
VMWare will use its own vmdk disk format.
24

25. Now lets take a look at how Citrix Studio connects with all the different hypervisors.
Citrix Studio normally resides on a XenDesktop controller en interfaces with the
different services running on the host.
These services take care of the brokering, manage the hosting connection and do the
MCS related tasks we mentioned earlier.
Studio is not the only way to interface with the core of XenDesktop, Powershell
CMDlets are also available directly.
When using Vmware, Citrix Studio talks to vCenter. vCenter therefore needs to be
made highly available if you want to make sure
You can always manage your environment or have Studio manage the VMs, maintain
the idle pools etc.
Should vCenter go down, you will not lose the current sessions, and any VMs that
have already registered themselves with the broker are still available for login.
vCenter in turn does the actual power on/power off of the VMs and the tasks related
to provisioning.
To get the most your storage and use the benefits on thin provisioning, Citrix
recommends using NFS datastores connected to the hypevisor hosts.
VMWare will use its own vmdk disk format.
25

26. Now lets take a look at how Citrix Studio connects with all the different hypervisors.
Citrix Studio normally resides on a XenDesktop controller en interfaces with the
different services running on the host.
These services take care of the brokering, manage the hosting connection and do the
MCS related tasks we mentioned earlier.
Studio is not the only way to interface with the core of XenDesktop, Powershell
CMDlets are also available directly.
When using Vmware, Citrix Studio talks to vCenter. vCenter therefore needs to be
made highly available if you want to make sure
You can always manage your environment or have Studio manage the VMs, maintain
the idle pools etc.
Should vCenter go down, you will not lose the current sessions, and any VMs that
have already registered themselves with the broker are still available for login.
vCenter in turn does the actual power on/power off of the VMs and the tasks related
to provisioning.
To get the most your storage and use the benefits on thin provisioning, Citrix
recommends using NFS datastores connected to the hypevisor hosts.
VMWare will use its own vmdk disk format.
26

27. Now lets take a look at how Citrix Studio connects with all the different hypervisors.
Citrix Studio normally resides on a XenDesktop controller en interfaces with the
different services running on the host.
These services take care of the brokering, manage the hosting connection and do the
MCS related tasks we mentioned earlier.
Studio is not the only way to interface with the core of XenDesktop, Powershell
CMDlets are also available directly.
When using Vmware, Citrix Studio talks to vCenter. vCenter therefore needs to be
made highly available if you want to make sure
You can always manage your environment or have Studio manage the VMs, maintain
the idle pools etc.
Should vCenter go down, you will not lose the current sessions, and any VMs that
have already registered themselves with the broker are still available for login.
vCenter in turn does the actual power on/power off of the VMs and the tasks related
to provisioning.
To get the most your storage and use the benefits on thin provisioning, Citrix
recommends using NFS datastores connected to the hypevisor hosts.
VMWare will use its own vmdk disk format.
27

28. Now lets take a look at how Citrix Studio connects with all the different hypervisors.
Citrix Studio normally resides on a XenDesktop controller en interfaces with the
different services running on the host.
These services take care of the brokering, manage the hosting connection and do the
MCS related tasks we mentioned earlier.
Studio is not the only way to interface with the core of XenDesktop, Powershell
CMDlets are also available directly.
When using Vmware, Citrix Studio talks to vCenter. vCenter therefore needs to be
made highly available if you want to make sure
You can always manage your environment or have Studio manage the VMs, maintain
the idle pools etc.
Should vCenter go down, you will not lose the current sessions, and any VMs that
have already registered themselves with the broker are still available for login.
vCenter in turn does the actual power on/power off of the VMs and the tasks related
to provisioning.
To get the most your storage and use the benefits on thin provisioning, Citrix
recommends using NFS datastores connected to the hypevisor hosts.
VMWare will use its own vmdk disk format.
28

29. Now lets take a look at how Citrix Studio connects with all the different hypervisors.
Citrix Studio normally resides on a XenDesktop controller en interfaces with the
different services running on the host.
These services take care of the brokering, manage the hosting connection and do the
MCS related tasks we mentioned earlier.
Studio is not the only way to interface with the core of XenDesktop, Powershell
CMDlets are also available directly.
When using Vmware, Citrix Studio talks to vCenter. vCenter therefore needs to be
made highly available if you want to make sure
You can always manage your environment or have Studio manage the VMs, maintain
the idle pools etc.
Should vCenter go down, you will not lose the current sessions, and any VMs that
have already registered themselves with the broker are still available for login.
vCenter in turn does the actual power on/power off of the VMs and the tasks related
to provisioning.
To get the most your storage and use the benefits on thin provisioning, Citrix
recommends using NFS datastores connected to the hypevisor hosts.
VMWare will use its own vmdk disk format.
29

30. Now lets take a look at how Citrix Studio connects with all the different hypervisors.
Citrix Studio normally resides on a XenDesktop controller en interfaces with the
different services running on the host.
These services take care of the brokering, manage the hosting connection and do the
MCS related tasks we mentioned earlier.
Studio is not the only way to interface with the core of XenDesktop, Powershell
CMDlets are also available directly.
When using Vmware, Citrix Studio talks to vCenter. vCenter therefore needs to be
made highly available if you want to make sure
You can always manage your environment or have Studio manage the VMs, maintain
the idle pools etc.
Should vCenter go down, you will not lose the current sessions, and any VMs that
have already registered themselves with the broker are still available for login.
vCenter in turn does the actual power on/power off of the VMs and the tasks related
to provisioning.
To get the most your storage and use the benefits on thin provisioning, Citrix
recommends using NFS datastores connected to the hypevisor hosts.
VMWare will use its own vmdk disk format.
30

31. If you take a look at the NFS datastore, you will find each provisioned VM to be in its
own folder. Actually Vmware has the tidiest folder structure, when you compare it to
other hypervisors, and it’s easy to see which files do what.
The Master vdisk is placed in a separate folder in the root of the datastore(s)
Directly linked to a pooled static VM are two vmdk files.
The first one is the Identity disk, and will not exceed 16 MB of space. In practice its
about half of that.
Then the second disk is a delta.vmdk, but this is actually a redirector disk. More on
than in a few slides.
31

32. If you open the identity disk vmdk you can see it’s readable text.
It contains many variables that have been set by Studio, to help make the VM unique,
even though it has spun off a master disk.
These variables are picked up by the VDA.
Amongst others, you will find a desktop ID there, but also the Catalog ID the VM is a
part of and the licensing server this VDA ties to.
32

33. If you open the delta.vmdk thats directly linked to the VM (i.e. configured in the VMX
file) you will see it’s plain text as well.
In there you can see it is beeing linked to a parent vDisk which is actually the Master
image you created the catalog with.
You can see the name of the disk is the same as the Catalog.
Secondly the redirector points another delta.vmdk which is actually the writecache.
33

34. When you boot the VM, you will see more files beeing created, of which two files a
REDO logs.
The delta.REDO is the actual writecache, and REDO files will be cleared on restart of
the VM.
Now these files are not the same as snapshots, since they only save the disk state and
not anything else that might have changed in the config of the VM, or it’s memory
and CPU state.
34

35. Should you copy a 1 GB file to the virtual desktop, you can actually see the write
cache grow.
The reason Studio sets up the writecache this way (using a redirector and REDO files )
is very smart because it will not have to do anything to clean out the writecache, it
just has to issue a restart of the VM (not a reboot)
35

36. Hyper-V’s architecture is similar for the Studio part of course, but Studio needs to
interface with System Center Virtual Machine manager to be able to communicate
with the Hyper-V hosts.
Just pointing Studio to SCVMM is not enough, you also need to install the SCVMM
Admin console on each XenDesktop Controller.
Same thing applies as with Vmware, you need to make sure SCVMM is highly
available to be able to have Studio manage the VM’s.
Hyper-V hosts prefer SMB datastores and they will use the VHDX format to provision
disks.
36

37. If you use XenServer, Studio can talk directly to the XenServer Poolmaster and needs
no management layer in between as the management layer for XenServer is more or
less embedded
Still you have to make sure the Poolmaster is always reachable.
When using XenServer, Studio again prefers NFS , and on this it will utilise the VHD file
format.
37

38. If you look at the file structure for XenServer, you will see that vdisks are created with
GUIDs as their names. It’s not clear from just the name or folder to hwat VM a disk
belongs.
To get that insight you’d have to go the command line route, and use “xe vm list” etc
to work out which is with. From the XenCenter GUI you can see what disks are
attached.
You also might notice the “Preparation” VM that’s beeing booted up during catalog
creating, during which it will do a mini sysprep and generate the identity disk info to
be used for the rest of the VM’s. The base disk itself will be copied from the Master
VM into each configured datastore.
38

39. Once you have the VM’s created you will see these pairs of the id and writecache
disks (a VHD chain is beeing built).
39

40. The last hypervisor we look at (and most certainly not the least!) , is the Nutanix
Acropolis Hypervisor.
AHV has been around for a while but we’ve only really started calling it AHV since
june last year when we released a new version of it at Nutanix .Next in Miami (which
will be held in Vegas in 2 weeks time btw).
We’re proud to announce full GUI based support for AHV in XenDesktop, which
includes the use of Machine Creation Services.
How does it work?
First of all you need XenDesktop 7.9, which has the latest version of the Provisioing
SDK installed on it.
Together with the Nutanix AHV plugin you install on every controller, you can now
have Studio talk natively to Acropolis.
Nutatix clusters are automatically highly available because of the distributed
architecture, so you only need to point Studio to the Nutanix cluster IP address and
you’re done.
It works the same way from that point on, and you create catalogs based on
snapshots, which will then lead to provisioned VM’s with ID disks and writecaches.
40

41. Under water we do a couple of things differently than the previsou 3 hypervisors.
We use a full clone approach, with copy on write functionality.
Each VM is linked to the master image, but will show up as the full vdisk, also the 16
MB ID disk is beeing attached.
These vDisks are thin provisioned, and while they show a usage of 10 GB in the above
example, the actual data usage will be much lower, since we deduplicate and
compress data on the storage level.
After every restart of the VM, the writecache disk is reset.
41

42. Here you see the actual logical files when looked at the datastore through a WinSCP
client, with the writecache disks at the top, and the ID disks at the bottom.
42

43. Image from Pixabay.com
https://pixabay.com/en/motor-engine-compartment-mustang-1182219/
So, lets dive into Provisioning Services.
43

44. VIDEO
Everyone remember this nice little Ardence video? It sure made an impact, since we
are still using this technology today, to literally deliver hundreds of thousands of
desktops to end user.
PVS is a streaming service and operates mostly on the network level.
It uses the exact same streaming method regardless of hypervisor, and as such does
not need to be adapted or learned new hypervisors.
As long as the hypervisors support PXE or boot iso methodes of booting the VM’s,
you’re good to go.
PVS actually intercepts the normal HDD bootprocess and redirects it over the
network to a shared vdisk.
The PVS servers you need actually only control the streaming of the vdisks, Studio is
still required to do the VM start/restart operations.
Pre-Existing VM’s can be used, or added using a wizard within PVS that sets the boot
order of the VM’s.
Before you can use PVS, there is an image conversion process you need to perform.
44

45. VIDEO
Everyone remember this nice little Ardence video? It sure made an impact, since we
are still using this technology today, to literally deliver hundreds of thousands of
desktops to end user.
PVS is a streaming service and operates mostly on the network level.
It uses the exact same streaming method regardless of hypervisor, and as such does
not need to be adapted or learned new hypervisors.
As long as the hypervisors support PXE or boot iso methodes of booting the VM’s,
you’re good to go.
PVS actually intercepts the normal HDD bootprocess and redirects it over the
network to a shared vdisk.
The PVS servers you need actually only control the streaming of the vdisks, Studio is
still required to do the VM start/restart operations.
Pre-Existing VM’s can be used, or added using a wizard within PVS that sets the boot
order of the VM’s.
Before you can use PVS, there is an image conversion process you need to perform.
45

46. Let’s take a look at PVS architecture.
PVS works with a separate infrastructure in addition to Studio, and also needs to be
sized correctly for the number of desktops it’s going to provision, and offcourse made
HA.
In practice you will always have more than one PVS server, and the number of
desktops you can stream per PVS server lies in the hundreds to a couple of thousand
depending on the PVS server’s specs.
A best practice is to use separate network segments or vlans to separate the (mostly
read-only) treaming traffic of the vdisks.
To allow a VM to read from a vdisk, it needs to be part of a Device Collection on the
PVS server, and the actual tie to the vdisk is done on MacAddresses.
This allows for quick swapping of vdisks, by just dragging and dropping.
A vdisk can be in 3 modes, of which Standard and Prviate mode are the most used.
Standard mode enables a 1 to many scenario, enables the writecache and makes the
vdisk read-only.
Private mode is mostly used to do updates to the vdisk, as it will make the vdisk
writeable, but only allows 1 VM to boot it.
There is a hybrid mode in PVS, but it is hardly ever used.
46

47. These vdisks are streamed to the VM’s, who can initiate the bootprocess by either
PXE or mounting a boot iso (BDM). PXE requires some extra DHCP settings (options
66 & 67 ) to be set, and might pose a challenge to use in an environment where more
services depend on PXE. BDM solves that problem, but needs more configuration on
the VM side, and the administraiton of the boot is.
The writes in PVS will go to the writecache, and this can be place on different
location. Most often used , is a local disk (the actual disk mounted to the VM, but this
can be configured as to be place on a local datastore).
Second option is to put the writecache in RAM, but this is a little tricky because RAM
is not as abundantly available as disk is, and when the RAM fills up, the VM will halt
or even blue screen. It’s the same thing that could happen when you run out of disk
space.
The 3 option is to place the writecache back on the PVS server, but this is hardly every
done as it will create serious bottlenecks and other management issues.
A 4th hybrid form has become more popular recently, as it first uses RAM, and when
that is full, it will overflow to disk. While it might sound great as it lowers IOPS
requirements at first, there are some downsides to it, because when the RAM
actually overflows, performance might go down. So sizing this correctly and keeping a
tight watch on it is very important.
47

48. The vDisk creation process is a bit more time comsuming than MCS since you need to
actually copy the entire disk contents to a VHD file using a wizard, after creating the
Master VM.
To be able to do this you need to install the Target Device tool on the VM as well as
the VDA. It is not part of the VDA.
When you do this, you can then run the Imaging Wizard to create the vdisk. The
Imaging Wizard also has some options to tune the VM by optimizing some settings,
but it is not very extensive.
Keep using the Best Practices guides and tools for that, that are available in the
community.
When you created the vdisk, you can then create a device collection (either manually
or using a wizard) an literally drag and drop a vdisk on top of it.
It makes the version management of the solution very easy. Switching back and forth
between vdisks only requires a reboot of the devices.
48

49. So how can we get the most out of these provisioning techniques.
49

50. So how can we get the most out of these provisioning techniques.
50

51. The most improtant thing is, to choose the right solution first.
We’ve created this little flow chart to help you.
51

52. Image acquired from Imageflip.com
https://imgflip.com/memetemplate/The-Most-Interesting-Man-In-The-World
While PVS didn’t really have any storage issues other than managing the local
writecaches, MCS did have issues when it was first relased since it was conceived in a
time when SAN’s were still roaming the earth freely and undisputed.
Problem for MCS is that because of this, it was not really a viable technology since
SAN’s run out of juice pretty quickly when a high number of VDI vms are hitting it for
IOPS.
This has become better over the years, but still when the number ofr desktops
increase, the overall performance for each desktop will go down since the SAN has to
divide the performance and capacity it has over more and more VM’s
So most of the time when people actually use MCS, they could only really do so when
utilizing local storage.
Now this brings up a whole lot of extra management complexity with it.
52

53. If you just use local storage, this means you first have to size right. How big will your
writecaches become, and how many VM’s do you intend to stick on a host. These
disks also need to be in some form of RAID setup to minimize failure impact.
Now when you configure XenDesktop to utilize local storage, this means you have to
configure each individual host withing XenDesktop.
And then as soon as you create or update a catalog, the vdisk needs to be copied to
all these hosts, extending image rollout times considerably, especially if you have a
large server farm.
53

54. A great way to solve this is to go the software defined route and opt for distributed
filesystem.
While this still leverages local storage (SSD’s preferably so it can’t bottleneck like a
SAN would), it is not managed as local storage.
The hypervisor just sees a single datastore, which also means you only need to
configure it only once in XenDesktop.
Net benefit of this is that it also just requires just a single copy to be made on image
roll out..
There however is a problem with this if you used just a typical run of the mill
distributed filesystem, that has no techniques to truly localize data) since it will not
be optimized for running a multi-reader scenario.
What will happen is that when the golden master is created, this process will write
the vdisk to the storage of the host that performs the copy. While the VM’s local to
that host will read the master vdisk locally, the other hosts in the cluster will access
the vdisk over the network. This could become a bottleneck when enough VM’s start
to read from the master. Even though the vDisk is probably replicated to other hosts ,
this is only done to assure data availability in case of a host failure. It will not
distribute the disk load balancing pursposes. At most, each host might have a small
cache to try to avoid some of the read traffic, but these caches are not optimized for
multireader scenario’s (only work for 1 VM reading its own disk) or the caches are
simply just too small to house the vdisk in the first place.
54

55. Nutanix solves this problem ahead of time by way of Shadow Cloning.
As soon as we detect that multiple VM’s (2 or more remote readers) pull data from
the vdisk, we mark the main vdisk as immutable which allows for distributed caching
of the entire disk. This is done on reads, block by block. This way each VM will
automatically work with localized data.
This not only relieves the network for reads (writes are local anyway), but it also
seriously improves performance.
This technology is enabled by default and requires no configuration whatsoever.
55

56. To summarize the benefits of running MCS on dsitributed storage:
First of all : no more multpiple image copies when rolling out. This seriously speeds
up deployment.
Secondly: no need to maintain multiple datastores, making things simpler.
Third: no IO hotspots anymore, increasing performance
56

57. To summarize the benefits of running MCS on dsitributed storage:
First of all : no more multpiple image copies when rolling out. This seriously speeds
up deployment.
Secondly: no need to maintain multiple datastores, making things simpler.
Third: no IO hotspots anymore, increasing performance
57

58. Image from imgflip.com
Here’s a before and after.
It’s obvious that it’s much simpler to manage hred 1 datastore than each indivual host
with local datastores.
With the technology of today this is now finally viable.
No need to change the hosting connection properties when you want to shutdown a
host for example.
58

59. Another couple of benefits of putting MCS on distirbuted storage:
1. Your VM’s stay moveable (i.e. vMotion or Live Migration) can be done, even
with local storage. With Nutanix’ Data locality the write cache data will be made
local to the new host automatically.
2. Reduced boot times. Not that this always is important since most idle pools will
be made ready ahead of the login storms, but it will also lower login times, and
improve overall end user perfromance.
3. Since we are no longer tied to a SAN infrastructure or require RAM caching
techniques to increase local IOPS, we can reach a much better scalability, since
it will be linear.
59

60. Shadow clones offer distributed caching of vDisks or VM data that is in a multi-reader
scenarios
Up to 50% performance optimization during VDI boot-storms and other multi reader
scenario’s.
60

61. Does this mean there is no beneif for PVS when using distributed filesystems?
Yes there are many!
But with PVS there was no issue with reading the master image, so that benefit
(Shadow Clones) will not apply.
What’s left?
1. No need to manage the local storage required for the writecache and make sure
it’s HA (RAID etc)
2. No need to worry about local disks filling up and crashing VM’s. It will just spill
over an leverage other hosts storage if needed.
3. No worry about local IOPS.
4. PVS-ed VM’s with a writecache stay movable. Writecache will follow the VM to
it’s new host thanks to Data Locality.
5. Simple configuration: just point create the writecache disk of the template VM
on the distributed datastore.
6. No need to use RAM caching technology to save on IOPS. This means more
RAM is available to VM’s, which means better scalability and higher VM density,
61

62. Does this mean there is no beneif for PVS when using distributed filesystems?
Yes there are many!
But with PVS there was no issue with reading the master image, so that benefit
(Shadow Clones) will not apply.
What’s left?
1. No need to manage the local storage required for the writecache and make sure
it’s HA (RAID etc)
2. No need to worry about local disks filling up and crashing VM’s. It will just spill
over an leverage other hosts storage if needed.
3. No worry about local IOPS.
4. PVS-ed VM’s with a writecache stay movable. Writecache will follow the VM to
it’s new host thanks to Data Locality.
5. Simple configuration: just point create the writecache disk of the template VM
on the distributed datastore.
6. No need to use RAM caching technology to save on IOPS. This means more
RAM is available to VM’s, which means better scalability and higher VM density,
62

63. Before we end the sesssion we have one more thing.
We have told you in the last 35 minutes what currently is available for MCS and PVS.
But this world isn’t standing still. What’s coming?
So we have a special guest today.
Please give a warm welcome to the man that actually builds this awesome MCS and
PVS technolgy: Jeff PinterParssons!
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64. 64

65. Not a product manager so no commitments
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