PVS vs. MCS in a VDI deployment
There’s a lot of debate in the engineering community on whether to use Provisioning Services (PVS) or Machine Creation Services (MCS) when deploying a VDI solution. There are clear differences between the two technologies, and depending on the type of deployment, important factors to consider when choosing which one to use.
MCS uses linked clone technology. This means that a snapshot is taken of the master template, which is then used as the parent disk for the clones (VDIs). This is a relatively simple method to deploy, and it doesn’t require any additional infrastructure.
Challenges of MCS
The main challenges of MCS are storage and scale-out related. With MCS, the clones and the parent disk must be on the same datastore in order to maintain link integrity. If the linked clones are distributed across multiple datastores, a copy of the master must be as well – substantially increasing the storage requirements for a deployment. For this reason, scaling out an MCS deployment can become difficult.
- MCS uses about 21% more IOPS than PVS. Depending on the network infrastructure, this may be an important factor to consider for maintaining consistent performance across the VDIs.
- MCS does not regularly “clean up” old master clones when deploying an update from a new snapshot. Instead, the old files must be manually removed in order to free up disk space.
PVS uses software streaming technology to deliver VDIs, requiring additional infrastructure to support the solution. PVS imaging wizard captures an image from the master machine, and then stores it in a VHD format (vDisk) on the Provisioning Server. The vDisk can then be shared (streamed) by multiple VDIs.
Technical Note: PVS utilizes a PXE boot method (BDM can also be used in the absence of DHCP) and a TFTP to stream the vDisk. Additional network configurations are required to allow PXE to work in the environment.
PVS is an elegant solution, and scales well in large enterprise-class deployments. Multiple PVS servers can be built out to balance the vDisk streaming load, providing redundancy as needed. And, with the introduction of caching to device RAM, the IOPS used by a PVS deployment can be greatly reduced (<1 IOP in some cases).
MCS is suited for small deployments (or lab scenarios) and is simple to deploy. But overall, PVS is the more robust and scalable solution for enterprise environments.
PVS requires more intensive planning, additional infrastructure, and more configuration to implement. However, once built it’s easy to maintain and requires very little maintenance. In most scenarios, it would be preferable to deploy PVS as opposed to MCS for the reasons outlined above.
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