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Vibration Killing Enterprise Disk Performance?
An anonymous reader writes "Is vibration killing disk performance? ZDnet reports on research that a carbon fiber anti-vibration rack increased random read performance by 56% to 246% and random write [performance] by 34% to 88%. Vibration is a known disk problem, but this is one of the few attempts to quantify its impact — which looks to be much greater than suspected."
Yes, already saw some crazed guy at Sun shout into an array of HDDs and it decreased performance.
http://www.youtube.com/watch?v=tDacjrSCeq4
..at SustainIT 2010, Turner had a really good analysis. Still some gaps - figuring out what frequencies hurt the most, and how individual drive types respond to what, is necessary followon. How various vendors' drive units transfer vibration from the rack into the unit, into the drive carrier, into the drive. That sort of thing. Now that the phenomena is identified, a lot more to do on it.
At the least, keep performance sensitive drives away from large sources of environmental vibration, such as your AC unit and so forth.
the article does not say that it affects SSDs, but that it affects the SSD value proposition (aka, if you can spend little $$$ on carbon rack enclosures and get a significant seek performance increase, spending the large amount of $$$ to go full-ssd might not be as cost effective).
-- the cake is a lie
I just want to point out that hard drives stopped using stepper motors decades ago. They've used voice coils since, which is basically an electromagnet and strong magnet which it deflects to various positions based on the field strength; in other words, it's continuous, not discrete like a stepper motor (though they can do microstepping as well). OK, so in a way, a voice coil is sort of like a stepper motor with only one phase, which is then microstepped...
Well you are half right, but so is the GP.
The GP's description is more accurate if you replace "stepping" with "accelerating".
The head does not move to a position based on field strength (open loop control). It is free to move on low friction bearings, the applied field strength accelerates the head. Closed loop control is needed to make it stop at the correct position.
A perfect example of why this type of joke flies right over the average /.er's head.
So perfect, indeed...
unless you really stacked the deck against steel racks - loose screws, hard drives not properly mounted...?
Depending on where exactly they are, loose screws might actually help you. Tight metal-to-metal connections are much better at transferring vibrations, especially the higher frequency ones, than looser connections, where some of the vibrational energy is converted into lower-frequency vibrations. Steel is insanely good at carrying vibrations over long distances, hence the old movie trick of listening to railroad tracks for a train in the distance, or tapping on pipes in Morse code to communicate your escape plans to the inmate several cells over. (At the risk of veering off-topic, neither of these tricks work nearly as well in real life as in the movies, but they do work. Well, at least the railroad tracks do. Since the MPAA hasn't found my gargantuan mp3 collection yet, I haven't had a chance to test prison telegraphy yet.)
One thing that has always baffled me is why racks and computer cases are made of metal to begin with. There are, of course, certain areas where you need steel or aluminum for strength or carrying waste heat, but wood or plastic would do a much better job of damping vibrations. There's a reason audio speaker cabinets are made out of crappy, soft stuff like particle board: you don't want the cabinet to resonate, and particle board does a wonderfully poor job of transmitting vibrations, which is why it isn't used in guitars, where you want strong resonance. There are also a wide variety of synthetic rubbers like neoprene and sorbothane that do a good job of absorbing vibrations. Neoprene is cheap, and sorbothane, while more expensive, is still affordable and does such a good job of deadening vibration that it feels remarkably like meat. (I happen to have a square foot of it sitting on the counter next to me, waiting to be used in some vibration-damping experiments with my scooter, but having RTFA, I think I'll try using a little bit to replace the rubber pads on the bottom of my external drive enclosures.)
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