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Data Storage It's funny.  Laugh. Sun Microsystems IT

Why Not To Shout At Your Disk Array 125

Posted by timothy
from the that's-what-your-subordinates-are-for dept.
Brendan Gregg of Sun's Fishworks lab has an interesting video demo up at YouTube demonstrating just how bad vibes, if expressed with sufficient volume in front of a rack full of disks, can cause a spike in disk latency. White noise, evidently, doesn't do them much harm. (Maybe they just feel awkward to get yelled at on camera.)
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Why Not To Shout At Your Disk Array

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  • Re:JBODs? (Score:5, Interesting)

    by Chris Snook (872473) on Friday January 02, 2009 @06:03AM (#26298147)

    ZFS implements software RAID on top of JBOD. The box full of disks itself need not have any RAID controller, and if you're using RAID-Z, it would probably be a waste of money to spring for one, unless you go for the super-high-end for performance reasons.

  • Re:Interesting... (Score:3, Interesting)

    by MichaelSmith (789609) on Friday January 02, 2009 @06:21AM (#26298195) Homepage Journal
    My first computer had a 6502 CPU with BASIC and a machine code monitor in ROM. I found that the cassette interface could be used as a sound card if I configured a tape player to record and play back at the same time. For the output channel any AM radio would do because the CPU only ran a 1Mhz and it was leaky as hell.
  • by Chris Snook (872473) on Friday January 02, 2009 @06:34AM (#26298263)

    Prior to the advent of skip protection in portable CD players, you could make them skip for several seconds just by shouting at them briefly, because it took much longer to recover from the vibration than the duration of the shock itself.

  • by freddy_dreddy (1321567) on Friday January 02, 2009 @06:55AM (#26298347)
    The plants publications never seems to die.

    Plants don't react to music, they react to the tiny shifts in air just above their stomata. The publication which reported this compared plants with music (read: vibrating air above the stomata) with plants in an enclosure without air vibrating (read:refreshing) above the stomata.
    The experiment shows a difference, even if there's air-movement simply because air "sticks" to the surface of plant's leaves in close proximity - behaving like a fluid. Normal air ventilation doesn't refresh this thin layer as optimal as vibrations caused by sound.
  • It's the Enclosure (Score:2, Interesting)

    by selectiontimeout (1443281) on Friday January 02, 2009 @06:55AM (#26298351)
    Well, partly at least. It's no secret that disk drives are sensitive to vibration as this video showed an extreme case. Keep in mind, since disk drives are spinning at 7200-15000RPM, they themselves create vibration that can affect adjacent drives. The drive enclosure can help reduce the problem with use of shock absorbers and vibration dampeners. Most drive enclosures nowadays, for cost reasons, are no more than just sheet metal wrapped around power supplies, fans and drives, which contribute to the problem.
  • by Anonymous Coward on Friday January 02, 2009 @06:59AM (#26298367)

    Secret Fact : Ultrasonic noise at low volumes is WORSE !

    It took weeks to testing to get to the root issue of WD Raptors dropping in head seeks on very high end raid cards in tiny head movement seek benchmarks, but padding each JBOD drive in acoustic foam (shooting range foam), or testing one drive at a time, instead of 4 or 8, (either method works) increased I/O per second by 40% in a rack chassis.

    40% more head movements per second if no ultrasonic noise entering drives !!!!!

    This is VERY VERY RARE INFO, and only I, the head of Gigabyte in Asia, and two engineers in california know of this discovery.

    And because I know no one on Slashdot will mod this up, and no one reads at 0 anymore, I can trust my astounding well researched secret shall remain secret.

    Its sadly 100% factual.

  • by Anonymous Coward on Friday January 02, 2009 @07:27AM (#26298477)

    Well, you can also use HDs as speakers:

    http://www.afrotechmods.com/cheap/hdspeakers/hdspeakers.htm

  • Warbirds? (Score:1, Interesting)

    by t0ny747 (849486) on Friday January 02, 2009 @07:44AM (#26298541) Homepage
    I was thinking ( more like dreaming ) about buying a HD video camera that uses a hard drive. I wonder how much the noise of flying in a WW2 era Warbird would mess with it. I flew in a B-25 and it someone screwed with my camera's ability to focus.
  • by Bengie (1121981) on Friday January 02, 2009 @10:28AM (#26299463)

    I'm not an engineer or absolutely sure about how the brain works with white noise, but I had a job that I worked at that when I entered the freezer section, it didn't seem loud at all. Actually, it so much didn't seem loud that the few times I had to enter it, I forgot my ear plugs until I saw someone else using them.

    Anyway, even though you couldn't really hear anything 'loud', if you tried to talk to anyway, you could barely hear them.

    On to my question. If you have enough high amplitude random noise that is effectively destructive interference, would this make an enviorment where low amplitude sound could not be hear or even mechanically sensed easily?

    I know using 'heard' may be incorrect in this context because perceived sound usually has no direct relation with what's mechanically going on with the sound waves.

  • by RobinH (124750) on Friday January 02, 2009 @10:59AM (#26299743) Homepage

    "Skip protection" on a hard drive is pointless. This is a fundamentally different scenario. With a CD, you can read the data *much* faster than you really need to read it, because you only need the data fast enough to convert it into sound. Plus you almost always know which piece of data needs to be read next, because the song is linear.

    On the contrary, with a hard drive, read speed is (usually) the bottleneck, so you want the data sent to the processor as soon as you can pull it off the disk. Also, hard drives are much more random access, so you can't guess the location of the next read and read it before the CPU requests it. The only thing you can do is cache frequently accessed data in memory, which the operating system already does.

  • by thethibs (882667) on Friday January 02, 2009 @12:36PM (#26300617) Homepage

    Disk drives have a resonant frequency

    I've seen dramatic demonstrations of this over the years. One that stands out was a test of a Bryant drive sometime around 1970. In those days a 2 GB drive was at the edge of the envelope and Bryant was test-marketing just such a beast. It consisted of eight four-foot platters mounted four to a side on a shaft going through a monster of an electric motor. The heads were mounted on arms whose positioning was controlled by hydraulic cylinders big enough to be used as shocks on a pickup truck. The whole thing would not fit in the back of that pickup truck.

    We were testing the thing with a program called the "Leese Bomb". Leese can identify himself or remain anonymous--I won't turn him in. The "Bomb" part was the nature of the test.

    Basic tests in those days would involve writing a whole track and then reading it back and comparing what was read to what was written. You'd do this a number of times with different patterns to capture not only faults in the surface, but any sloppiness in the head control. The Leese bomb went one better.

    It would write to the outside track, write to the inside track, read the outside track, read the inside track, and then compare. If the comparison failed it would repeat the test, and keep repeating untl it succeeded, counting the failures. If the test succeeded it would index the test both inward and outward so that the tracks tested would move toward the middle, cross, and continue. This test was superior in that it would capture dynamic flaws in the system as the distance the heads moved, and the time to move varied from max to zero.

    In the case of the Bryant Drive (and, accidentally, an innocent Ramac drive at Caltech), the test found a resonant frequency. When the heads overshot their mark causing an error, the test stayed on the back and forth pattern, reinforcing the resonant motion with each cycle of the test. The drive started walking across the test floor in three-inch hops, but not for very long. In a few seconds, one of the shafts broke and one of the platters, a 500 pound disk rotating at 2400 rpm broke through the front of the unit and flew across the building until it was stopped, explosively, by one of the steel columns supporting the roof of the building. Miraculously, no one was hurt.

    We gave up on Bryant for that application. Not long after that, CDC introduced its 200MB drives, and they passed the Leese Bomb with flying colours. Ten of them didn't take up any more room, or cost more, than the big Bryant, so our client was happy to go with that solution.

    In any case the lesson is that, if it has moving parts, resonance is an issue.

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