Another battle royale: SAN vs. local storage for VDI

The "experts" are at it again and I feel that it's my duty to set 'em straight.
Written by Ken Hess, Contributor

If you've followed my posts, you know that I love the so-called "experts" and their often media-informed opinions about technology. It's good entertainment for me when one of them says that technology 'A' is the right answer and technology 'B' is too slow/expensive/difficult to manage/legacy or whatever the latest buzzterm is for them to use. Often my buddy, Jason Perlow, and I get together on a podcast, phone or via IM and give these guys a good going over. Sometimes we make it public and sometimes we don't. Yesterday, I received a notice for a discussion about SAN vs. local storage for VDI in my email that features Brian Madden and Gabe Knuth. Well, of course, I had to read it.

A moment of divergence: If you read Brian Madden's bio, you'll see that he considers himself to be a world-renowned desktop virtualization expert. OK, let's go with that. Though he lists no practical data center or technical experience, he has written a lot about desktop virtualization. I suppose one can become an expert as an observer. I know a lot of football (American football) experts who've never spent one moment on the field as a player--so, it happens.

The transcript is very hard for me to read*, so I searched for the original post and found it. I also found Ron Oglesby's rebuttal, where he says Brian is wrong. Although I don't know Ron nor his complete background, he does seem to have some practical technical experience behind him. He also posts that he is a "Cheif Solutions Architect at Unidesk," as his title. I won't fault him too much for not being able to spell "Chief" correctly.

My thought is that, again, there's no single right answer for this technology question. There are pros and cons for both. And, consequently, I think both Brian and Ron are wrong. But, they're also both sort of right too. But, it's their "all or nothing" campaign that makes them more wrong than right.

How can they both be wrong when Brian says, "Local" and Ron says, "SAN"?

The reason is that it depends on the VDI user--you know, the person for whom VDI is supposed to serve. For people who use Word, Excel, Outlook and Internet Explorer (or their Linux counterparts, if anyone's using Linux VDI), then they can just boot from SAN and use that image. Heck, they could even use a shared Windows image--and contrary to what Brian says, it actually can be done. There are companies doing it. Parallels is one of those companies.

However, there are cases, rare though they are, where you'd want a user to have a locally-stored image. Those users require a "bigger" desktop in all instances--more RAM, more disk space, more CPU, more network bandwidth and faster disk access.

It's not really an all or nothing question or answer. If you're moving to a VDI solution, you'd better take the type of user workload into account or you're going to have some very unhappy users pounding on your door. In a perfect world, you'd need only one disk solution. The world is far from perfect, so you'll need local storage (I recommend SSD) and SAN. You'll possibly also want some other type of network attached storage (NAS) for storing documents and other data files that doesn't require SAN speeds.

You see, for most users, speed isn't all that critical. Once the image boots, everything required is in memory. Your biggest bottleneck isn't going to be disk I/O but network bandwidth. However, you can control some bandwidth problems by using VLANs or other network segmentation to separate "boot storm" traffic from regular data flow.

It is for the reasons I've given that VDI is very expensive. You need local storage for some users and SSDs aren't cheap. You need SAN for almost everyone else, which isn't cheap. And, you'll need NAS for longer-term or static storage. You'll also need a good backup and restore system for your data as well as your disk images unless you use a single desktop image (or a few master images).

The best scenario for a one-to-one (one user to one desktop image) is to have a master image that everyone gets a copy of for their very own. No local data and no local changes are possible on that desktop image. This way, you'll only have to preserve one desktop image or a small set of images based on user function and a few local images for those who require those locally stored desktops.

It isn't as simple as these guys tried to make it. It never is.

A bit of real world experience helps a lot.

What do you think about local vs. SAN storage for booting and storing disk images? Do you think it's all or nothing or do you think it's a mixture? Talk back and let me know.

*It's very hard to follow the language in it. I had no trouble with the actual words.

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