I think we are all right. Unfortunately, there is no perfect storage device. Customers have different priorities and that drives them to make different purchasing decisions.

Like most things in life, purchasing a storage device is a compromise. For example, it is challenging to bring fine grained data placement control together with a feature such as pointer based dependent copies or deduplication.

You are again correct that emulation or virtualization is not free. Virtualization (for servers, storage, or anything else) inherently introduces overhead, but lots of customers are making the decision that is is worth it for the benefits they get. I am not making a judgment as to which features are better or more important. Customers tell the vendors everyday when they make a purchase. Maybe a little less frequently in 2009.

– Jesse

On a strictly technical level, Steve is right — all modern storage arrays do a certain amount of emulation of one sort or another. He’s right in a pedantic sort of way. But I think he might have missed the point I was trying to make.

And, of course, to your point, if the benchmark is good enough — and delivers acceptable results — does it really matter? You’re right as well.

So, let’s try this again.

Certain emulation schemes can behave differently than one would predict if one was using a more physical approach. If you’re aware of those differences, and they don’t matter to you, no problem.

BUT (!) the vendors who offer such schemes make little effort to highlight differences that might be significant in some situations. And that’s where I raise the flag.

Familar with short stroking? Doesn’t work so well on many of these emulated approaches. Want to place data on the outer tracks to maximize bandwidth? Sorry, no can do in most situations.

Or, my personal favorite, dramatically declining performance numbers as the device fills up. Now, in a physical storage world, you wouldn’t expect THAT to happen, would you?

Or perhaps an array that’s scheduled a defrag/reclamation task in the middle of the day? Not something we’d expect a more physical array to do, right?

There’s more to the discussion, but I think you get my point.

Nothing wrong with emulating per se — but I think harm is done when it’s offered as “no differences whatsoever” as opposed to exposing key differences and helping people make informed choices.

Just to be clear, EMC offers an emulated block device (iSCSI on Celerra) as well as native block devices. We’re quite conversant on the key differences between the two.

Hope this helps.

– Chuck

now all you need to do is point out that benchmarking is about as Pavlovian as you can get for marketing organizations. Get someone to salivate about “benchmarks” and surely their checkbooks will follow. Happens in the AMD vs. Intel, ATI vs. nVidia, etc. etc. debates all the time. It’s almost akin to determining who’s technology is “better” all the while using the same hardware. It’s about the implementation of technology, not necessarily the underlying hardware components. (caveat: sometimes the hardware makes an extreme difference in results. witness EFD vs. mechanical disk; global cache vs. localized cache; etc. etc.)

cheers,

Dave

Thanks for reading. In the long term, I think this is about storage Quality of Service functionality. That seems like the only practical way to get the performance guarantees administrators want with reasonable management overhead.

I am working on a few more posts about benchmarking. I think it is a great topic and one that is quite challenging for the storage administrators.

– Jesse

Thanks for adding to the conversation. I agree with you on the next step beyond the “real versus emulated” idea: Who cares? The thing that matters is that the storage works in the use case intended.

I hadn’t read your blog in the past, but I’m subscribed now. Good stuff here!

Stephen