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Calling for an End to

Unrealistic SSD vs HDD IOPS Comparisons

by Zsolt Kerekes, editor - May 29, 2008

How Much Hay Has Your Car Been Eating Lately?

I've been publishing articles about the SSD market since the 1990s - so maybe that's why something in my brain snapped yesterday when I was reading yet another new article from an SSD vendor about the server acceleration which you could get from their product.

Because the only competition it mentioned was hard drives.

Enough is enough! - I said.
I can't remember whether the article claimed their product was 300x or 500x faster in random IOPS than a 15K SAS hard drive - but as the IOPS in a hard drive haven't changed much since the appearance of the first 15K RPM products in EMC's CLARiiON systems in 2002, and as there may never be a 20K RPM drive... The long and the short of it is that every month the fastest SSDs get better - while the fastest hard drives remain exactly as fast as they were. So the HDD versus SSD random IOPS gap gets wider. We haven't learned anything new!

I'm not denying that these comparisons have been useful in the past. And they are still useful when a single 2.5" SSD for example is being compared with a single 2.5" hard drive. But as I wrote in an article in 2003 when you're looking at what a fast rackmount SSD can do for you - you should be calculating how many servers you can save / or would need to add to get to the same 3x application speedup - not how many disks.

It's understandable that people refer new products to an assumed common frame of reference.

I'm sure that a century ago when the first car owners were talking to their neighbors - they must have made comparisons like - how much faster they were than a horse.

"It's amazing. Unlike my old horse my new car doesn't get tired. And I don't need pasture or hay to make it go - just a few bottles of gas."

And you didn't get the same stinking mess in the city streets either. (At the time the Sherlock Holmes stories were being published in the Strand Magazine in 1892 - there was a "green" market carting horse dung out of London to stop the streets becoming impassable.)

I think I'm safe in assuming that the last time you bought a car - you didn't compare its speed or fuel consumption to a horse. Am I right?

Of course you didn't. You compared it to other cars!

It's a sign of a maturing market when there are enough products around to compare them to each other, instead of comparing them to what came before. And we have reached that time with SSDs. It's taken 30 years - but that's another story.

This new wave of comparing SSDs to each other kicked off with the article RAM SSDs versus Flash SSDs - which is Best? - which included views from leading SSD oems on both sides of the fence. And other articles have demolished the myths about SLC flash SSDs while highlighting the risks of using MLC flash in inappropriate server applications.

In my view comparing SSDs to HDDs does not give you a useful picture when you're looking at options in the server acceleration market.

Although I expect that such weak comparisons will be sprinkled in lite weight SSD articles for the next few years - it's time for some stronger seasoning. It's time for more articles by SSD vendors to say how their products and technologies compare with other SSDs.

...Later:- some companies are still doing it... ..In contrast - here's a fact filled vendor-neutral white paper (published November 2008) - which provides useful measurements and comparisons...

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...Editor:- talking to an SSD company (Oct 2011) about why they should stop using outmoded hard disk comparisons in their marketing communications.
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the Problem with Write IOPS in flash SSDs
Random "write IOPS" in many of the fastest flash SSDs are now similar to "read IOPS" - implying a performance symmetry which was once believed to be impossible.

So why are flash SSD IOPS such a poor predictor of application performance? And why are users still buying RAM SSDs which cost an order of magnitude more than SLC? (let alone MLC) - even when the IOPS specs look superficially similar?

This article tells you why the specs got faster - but the applications didn't.
the problem with flash SSD  write IOPS And why competing SSDs with apparently identical benchmark results can perform completely differently. ...read the article
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Have you ever wondered how the amount of flash inside a flash SSD compares to the capacity shown on the invoice?

What you see isn't always what you get.
nothing surprised the penguins - click to read  the article There can be huge variations in different designs as vendors leverage invisible internal capacity to tweak key performance and reliability parameters. ...read the article
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