I recently posted on how Provisioning Server helps to offload and reduce the amount of IOPS your underlying storage needs to support in order to maintain sufficient performance of your XenDesktop VDI deployments (see link here). One of our Citrix Engineers asked me to also cover MCS and to explain how Citrix is actively working to achieve the same kind of results even when using MCS and a "master image" VM.

So here it goes!

It's important to understand the goal-- to minimize the amount of horsepower and cost needed for the underlying storage in a XenDesktop VDI deployment. As described in the PVS post linked above, the "issue" with things like Citrix's MCS or VMware's Linked Clone technology is that it relies on a "master image", and that image gets pounded with IO. To work through this, lots of customers invest heavily in their underlying storage specifically for this image. And this is absolutely acceptable; a STRONG and highly available storage environment is critically important here and in all other virtualized environments. But again, the goal is to minimize the COST of the necessary horsepower the deployment.

This is where Citrix's XenServer Intellicache comes into play (not to be confused with HDX Intellicache, which does operate similarly but specifically for bandwidth and end user experience optimization). This technology leverages the LOCAL disk drives in a XenServer host to help "offload" disk operations. Once the first virtual machine boots and begins to read against the master image, XenServer caches the master image data on the local disks configured for Intellicache, and future reads to the image are then satisfied locally. This tremendously reduces the IOPS load against your shared storage array.

And because the cost of local drives is more affordable than the drives in an Enterprise quality storage array, you can cut the cost of your deployment (which IS THE GOAL). You can even invest in solid state drives (they rock, by the way) for the local server and drive the performance that much higher, at a lower price point.

Intellicache also offloads and reduces the consumption of bandwidth on the storage network-- and if you use NAS for your shared storage with support for NFSv3, this can help you overcome the "single TCP session" limitation of NFSv3.

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