When you want to migrate from Citrix 6.5 to Citrix 7.x, you need to make some decisions and one of the most important one is to choose whether to go for PVS or MCS. I have done some searches and found a lot of articles but some of them are really good and based on the real experiences. Have a look at this : (when you are making decisions)
From Barry Schiffer web site, he explains and puts things in a different perspective for anyone making this decision;
Let’s start with the first decision in the tree in which we ask the question about using a XenDesktop only, XenApp only or mixed platform. The reason for this is that, before XenDesktop 7, it wasn’t possible to do MCS for XenApp load. Since XenDesktop 7 it’s actually possible to use Machine Creation Services for XenApp.
In the old days we were worried about boot and logoff storms because of the amount of IOPS this generated on our expensive shared storage systems. If so we would advice to use Provisioning Services because of better IOPS caching possibilities.
Lots has changed in the past few years but the IOPS load is pretty much still the same, yet the decision making process changed. The reason for this change is that we now have more knowledge about the amount of IOPS and vendors jumped in and created new solutions offering huge amounts of IOPS on central or local storage.
On the hypervisor level we are now able to do live storage migrations. This helps us when we need to perform management tasks and don’t have the time to wait for all of the users to close their sessions.
For Machine Creation Services it’s highly recommended to use a storage solution that offers the ability to utilize thin provisioning. This way we only use as much data as we need for write caching. If we don’t utilize thin provisioning each target will use as much disk space as the configured base image.
Another decision is the need for dedicated aka persistent virtual desktops. If we need persistency you were forced to use Machine Creation Services. The reason for this decision was based on the fact that Provisioning Services falls back to Server Side caching when the cache had to be persistent. This method of caching results in a crappy desktop performance.
Since the introduction of Citrix Provisioning Services 6 we are able to offer persistent caching on the local target hard disk, which pretty much solves this issue. We therefore are now able to utilize Provisioning Services and Machine Creation Services for persistent desktops.
Physical vs Virtual
When we have a demand for physical virtual desktops we still need Provisioning Services. Machine Creation Services integrates on the hypervisor storage layer and therefore can’t be used on a physical target. This is the simplest decision of them all!
Advanced Image Management
As a reader of my blog you should already know that I like automation therefore I would never update images but instead rollout a new image. This way I can retest my image deployment every once in a while . Not of lesser importance I can always go back to my deployment run books to see how a certain component was installed for troubleshooting purposes.
If you care about image versioning and do a lot of image updates Provisioning Services is your way to go. Provisioning Services gives you greater flexibility to work with image versions and updates. Not everyone agrees with me on this one so I have decided to keep this out of the decision tree for now.
Multiple image locations or multiple images
This section has been added after publishing the article because the decisions attracts some attention, mostly by the guys from Atlantis Computing which must mean this market space has their full attention:). When we look at the Provisioning Services (PVS) architecture we have a central image store, the PVS server, for the sake of keeping things simple I’m not going into where PVS gets the image from local, filer, DFS et cetera. Machine Creation Services (MCS) works on the storage layer and places the image on each datastore which is used for targets.
When I create a new image or update an image with PVS I just change the pointer for each target and I’m done. With MCS that’s different, MCS first creates a single imagefile from a VM snapshot and when finished copies that image to each datastore. This process takes up CPU, IO and network resources and can take up to an hour in one of my production platforms (SSD 10Gbit et cetera).
So imagine a VDI cluster with 12 hosts with locally presented storage, this could be SSD, FusionIO or just as easily Atlantis ILIO. This would mean we have, at least, 12 storage datastores. With PVS this all stays simple, PVS is the central image location. With MCS this would mean we copy the base image to 12 different datastores.
Aside from the multiple image locations think about what happens if you have more then one image. This is not uncommon in enterprises, an example could be a VDI image, an RDS image with Internet Explorer 10 and one with Internet Explorer 11. This would mean that for MCS we copy not one image to 12 datastores but three images to 12 datastores. Think about the time and resources going into maintaining those images.
My decision would therefore be to stick with Provisioning Services when you have more then a couple of datastores or images.
Thanks Barry Schiffer, this is an awesome article.