There are so many disruptive VMware technologies in the VDI space that sometimes is hard to keep up with them all. I am looking forward to few of them, such as the VMware Distributed Storage and Space-Efficient Sparse Virtual Disks.
At same pace the storage industry is being transformed and now most storage solutions on the market are leveraging the performance of flash memory in it’s many form factors. Some vendors have Solid State Drives, other PCIe card devices, and other vendors utilize the PCIe cards in their scale-out solutions – but at the end of the day they are all using flash memory.
Because of this transformation on the hardware and software stack much of the architectures and methodologies to deploy VMware View and VDI solutions in general are also changing.
The the use of dedicated Solid State Drives to host VMware View Replica disks is not something that I would recommend anymore for a greenfield deployment. Just to remind you that I was once advocate of the Dedicated Replica Datastores and wrote many articles about it (How to offload Write IOs from VDI deployments).
As an example of this paradigm shift is the work that my VMware colleague’s Tristan Todd and Mac Binesh at the Technical Marketing Team, and Daniel Beveridge at the CTO Office have been doing with PCIe Fash devices.
They team used couple Virident FlashMAX II cards (The Virident FlashMAX II in my Lab) to deploy Linked Clone non-persistent desktops using View Composer. The other well-known vendor for these cards is FusionIO, but there are others.
Performance will vary from vendor to vendor, but in general a single Storage Class Memory (SCM) in a PCIe form factor is able to ingest hundreds of thousands of IO requests. These PCIe cards are normally low capacity (more capacity, more $$$) but in this scenario where Linked Clone non-persistent desktops are used, the capacity is not something to worry about.
Here is the interesting part of the tests.
Because of this extraordinaire capacity to ingest IO requests the team started to play with the amount of RAM assigned to each virtual desktop in each host. They started to reduce the amount of RAM from an initial 2GB down to 512MB, while maintaining Windows Swapping at the 2GB size.
The expected result is obvious and Windows started to heavily swap to disk when no physical memory is available.
“To optimally size your paging file you should start all the applications you run at the same time, load typical data sets, and then note the commit charge peak (or look at this value after a period of time where you know maximum load was attained). Set the paging file minimum to be that value minus the amount of RAM in your system (if the value is negative, pick a minimum size to permit the kind of crash dump you are configured for). If you want to have some breathing room for potentially large commit demands, set the maximum to double that number.”
What the they found out using VMware View Planner is that they were able to run 250 virtual desktops in a single host assigning only 512MB RAM to each desktop while maintaining disk latency under 1.0ms.
These numbers have a major impact on VDI deployment CAPEX cost. The table above clearly demonstrates that reducing the amount of RAM per desktop also reduces the Host RAM Active memory (duh!).
Ultimately, it also means that it is possible to drive consolidation upwards because less memory is required per host, as long there is enough CPU GHz available to host desktops. I would not be surprised to soon see hosts supporting 500 desktops with approximately 180GB physical RAM only.
What about CBRC or View Storage Accelerator?
I would argue that View Storage Accelerator isn’t of much importance anymore in this architecture. However, if you prefer desktop read IOs from the replica disk being served in microseconds rather than milliseconds I still recommend the use of CBRC.
This is amazing and breakthrough, but there should be caution when designing and deploying such solution.
Fault Domain – In a solution that only relies on local host PCIe devices the fault domain is the entire host. When running 250 or 500 desktops in a single host, what would be the business impact if this host fails? There are few possible solutions, such as having spare hosts ready to take on the workload, but ultimately it’s a business decision.
Non-Persistent Desktops – An architecture that leverage local host PCIe devices does not provide reliability for persistent desktops where users may need the ability to deploy their own applications and persist them across sessions. If the PCIe device panics or dies the user desktop would be lost without a proper image backup. Put here VMware Mirage technology and this may not be a hurdle anymore.
The VDI architectural scenario is definitely changing, and changing fast. In this new scenario there is no need for Dedicated Replica Datastores anymore. It’s all Flash; all local to the hosts, no intermediary caching.
Some other impressive numbers are related to the ability to quickly provision and recompose desktops using Storage Class Memory. I personally think these numbers are not very important for most VDI deployments as Administrators normally provision or re-compose desktops over weekends or overnight. Still an impressive number!
Finally, if you want to learn more about the architecture tested, the results and other technologies that may provide similar results I would urge you to attend session EUC1190 during VMworld. VMware US is over, but you still have a chance to attend the session at VMworld Barcelona… and in the near future I will probably talk more about how VDI architecture is changing.