CSI: VDI
Posted Tuesday, April 12, 2011 in Technology 0 comments
VDI and CSI
So I’m watching the news the other night and this ad for some new cop show comes on (it was CSI: Abercrombie and Fitch, I think). It looked pretty formula – attractive, fashion conscious 22 year old forensic pathologist meets dead guy, becomes fascinated with dead guy’s life, and solves the mystery of his untimely demise, all in an hour. Formulas can be convenient, since they tend to be based on past, proven experiences, and Hollywood is a perhaps annoying example of that. I tend to day (or night) dream about storage a lot when I’m winding down at the end of the day, and got to thinking about how formulas apply in an area I’ve been spending a lot of time on lately: virtual desktops.
If you’re about to embark on a virtual desktop infrastructure (VDI) project, what formula are you using to determine the storage configuration you need on the back end to meet your performance requirements? Do you have a variable in there that accounts for the storage performance degradation you’re going to experience when you use a standard, SAN array as the storage back end for a VDI configuration? Does that variable assume that you’re going to get at least 30% fewer IOPS out of your storage configuration than you have been getting with that same array when it’s attached to physical servers? Have you budgeted for the additional storage hardware (spindles, solid state disk (SSD), etc.) that you’ll need to bring that performance back up to where you need it to be?
If not, you might want to consider the following:
- Anytime you have virtual machines (VMs) residing on a physical server, the I/O pattern that that server generates is going to be much more random and write-intensive than it ever was when it was just a physical server running one application
- Current disk technologies, including both spinning disk and SSD, perform at their worst with very random, very write-intensive workloads – this is the phenomena that results in the storage performance slowdown in virtual environments because rotational latencies and seek times start to dominate data transfer times
- The more VMs that reside on a host, the more random and more write-intensive the I/O pattern becomes, leading to the realization among graduates of the “school of hard knocks” that you need a bigger (translate: more expensive) storage configuration in virtual server environments than you do in physical server environments, and you need an even bigger (translate: even more expensive) storage configuration in most VDI environments
Bottom line: make sure you test storage performance with a small, VDI pilot project so you can start to get an idea of what the “storage degradation variable” and storage budget will need to be for your environment.
You can address this problem in one of two ways: throw hardware at it or throw software at it. Throwing hardware means buying more spindles and/or buying faster storage technology (FC instead of SATA, SSD instead of spinning disk, or enterprise-class storage arrays that use components like PAM modules, etc. to help speed up storage performance). Prepare for some heavy lifting in the storage budget area if this is the approach you plan to take, but at least now you won’t be surprised.
The other way is throwing software at it. If an approach that increases the IOPS you get out of your existing spindles by 300% - 500% (regardless of whether they are spinning disk or SSD), works with any heterogeneous block-based storage, and is a simple install at the hypervisor layer (no software in individual VMs or virtual desktops) sounds interesting, you might want to check us out at www.virsto.com. We’ve got other interesting things to say about thin provisioning and snapshot/clone technology that again, are driven by software and available on top of any heterogeneous storage, all of which are available with a single virtual disk type: the Virsto vDisk. Count on bringing your cost/desktop back into the range that will get your VDI project moving again.
Who knows? Instead of the next big show being about autopsies of derailed VDI projects (CSI:VDI?) it might be more along the lines of “Are You Smarter Than A Physical Server Storage Analyst?”…!
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