Home > Performance, Value, Virtualisation > Data Storage for VDI – Part 9 – Capex and SAN vs DAS

Data Storage for VDI – Part 9 – Capex and SAN vs DAS

I’d intended writing about Megacaches in both the previous post, as well as this one, but interesting things keep popping up that need to be dealt with first. This time it’s an article at information week With VDI, Local Disk Is A Thing Of The Past. In it Elias Khnaser outlines the same argument that I was going to make after I’d dealt with the technical details of how NetApp optimises VDI deployments.

I still plan to expand on this with posts on Megacaches, single instancing technologies, and broker integration, but Elias’ post was so well done that I thought it deserved some immediate attention.

If you havent done so already, check out the article before you read more here, because the only point I want to make in this uncharacteristically small post is the following

The capital expenditure for storage in a VDI deployment based on NetApp is lower than one based on direct attached storage.

This is based on the following

Solution 1: VDI Using Local Storage – Cost


Solution 2 : VDI Using HDS Midrange SAN – Cost

$860,800, with array costs of approx $400,000

Solution 3 : VDI Using FAS 2040 – Cost

860,000 – 400,000 + (2000 * $50) = $560,000

You save $54,000 (about 10% overall) compared to DAS and still get the benefits of shared storage. That’s $56,000 you can spend on more advanced broker software or possibly a trip to the Bahamas.

Now if you’re wondering where I got my figures from, I did the same sizing exercise I did in Part 7 of this post but using 12 IOPS per user and using 33:63 R:W ratio. I then came up with a configuration and asked one of my colleagues for a street price. The figure came out to around $US50/desktop user for an NFS deployment, which is inline with what NetApp has been saying for about our costs for VDI deployments for some time now.

Even factoring in things like professional services, additional network infrastructure, training etc, you’d still be better off from a up-front expenditure point of view using NetApp than you would with internal disks.

Given the additional OpEx benefits, I wonder why anyone would even consider using DAS, or even for that matter another vendors SAN.

  1. Robert Kadish
    July 28, 2010 at 4:45 am

    I agree with your cost assumptions local storage does cost more. We have been doing a lot of work with Liquid ware labs and most of the vdi delployments we are looking at have at least 30 to 50 IOPS per user.

    For what it’s worth.

    • July 28, 2010 at 7:44 am

      Wow, 30 – 50 IOPS, that’s a lot higher than the 8 – 12 steady state IOPS I’ve been hearing. Is that peak I/O during things like boot/virus checks or is it steady state ?

  2. Mihai
    July 28, 2010 at 5:38 am

    Yes, of course using classic DAS is more expensive, but you convienently forget about the option of using local SSDs with Linked Clones for automated non-persistent desktop pools…

    • July 28, 2010 at 7:54 am

      Thanks for pointing this out, though the omission wasnt convenient 🙂

      I was in something of a rush to get the post out in reply to Elias Khnaser as it addressed the points I was going to raise later. Ideally I wasnt going to do the capex vs opex comparisons until I’d gone through all the technology options in more detail, but I decided it was relevant enough to jump the gun a little here.

      I’ve still got a stack more posts to go and SSD’s for the use case you pointed out is slated for about 3 to 4 posts time which about a month or two away looking at my current travel/work schedule. Part of the reason for this is the research for the post on Megacaches which includes a reality check on SSD performance is taking me a lot longer than I thought.

      If you’ve got some real world costings for your use case I’d be happy to include them in one of my followup posts, or feel free to add them to the comments here.

      Once again, thanks for your comments, if you, or anyone else, thinks I’m deliberately leaving out relevant material or something that contradict my conclusions, I urge you to call me on it.


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