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Why Not To Shout At Your Disk Array
Posted by
timothy
on Fri Jan 02, 2009 03:58 AM
from the that's-what-your-subordinates-are-for dept.
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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Youtube comments (Score:5, Funny)
he's like the crocodile hunter of loud server rooms
Re: (Score:3, Funny)
...always made me laugh.
Yeah, they get you less tense.
Re: (Score:2)
The video was pretty freaking hilarious as well!
Re: (Score:2)
por que no?
Maybe this is why Windows gets slower all the time (Score:5, Funny)
People yelling too much at their computers
Re:Maybe this is why Windows gets slower all the t (Score:5, Funny)
hmm, bit of a chicken and the egg scenario there, isn't it?
is it slow because you yell at it, or do you yell at it because it is slow?
Either way, in the end it only degenerates into a downward spiral, where the computer gets slower and slower, while you get more and more pissed off at it and yell louder...
Parent
Why isn't this under idle? (Score:5, Informative)
It's been known for a long time vibrations are not good for discs (see notebooks). Even by early 90s music CDs had skip protection. If a disc skips, latency will of course momentarily increase. And with tolerances down even further, it's probably worse than back then.
In 10-15 years it won't matter anyway, almost everything will have SSD by then.
Re:Why isn't this under idle? (Score:5, Interesting)
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.
Parent
Re: (Score:2)
Yep. Even on my modern CD sound system with skip protection (cache), if I crank the volume up loud enough, the speakers will eventually vibrate the mechanism for so long as to cause the player to shudder and skip.
Re: (Score:2)
Are you sure about this?
Let's say that I have my phone in my pocket, will that not affect?
Yes I agree that plain vanilla yelling will probably have no effect whatsoever. BUT what about radio waves?
Not to say it will stop me from buying SSD, just wondering out loud.
Re:Why isn't this under idle? (Score:5, Funny)
There's BAD vibrations, and then there's GOOD Vibrations. [youtube.com]
Parent
Re:Why isn't this under idle? (Score:4, Interesting)
"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.
Parent
Re: (Score:2)
Dear $DEITY don't start pulling that apart, I'm joking.
Interesting... (Score:5, Insightful)
Re:Interesting... (Score:5, Funny)
I would say yes. When I was a teen my mother walked into my room and started moaning about the mess.
Right then, windows blue screened and later I found the hard drive was completely dead. (Think it was a 15GB Maxtor or thereabouts) That cost me some pocket money to replace at the time.
If you have women living in the house, factor this into your backup procedure.
Parent
Re: (Score:3, Funny)
Re:Interesting... (Score:5, Funny)
You made me wonder; if the the effect could be detected and "read", a you say, it would be possible to use it as a way of transmitting information to the computer by shouting at it.
I then remembered microphones.
Parent
Re: (Score:3, Interesting)
This Discovery (Score:5, Funny)
How this guy actually made the discovery.
He must have let off quite a bit of steam towards that rack.
Re: (Score:3, Funny)
'The very existence of flame-throwers proves that some time, somewhere, someone said to themselves, You know, I want to set those people over there on fire, but I'm just not close enough to get the job done.'
George Carlin
Re: (Score:2)
Not to be a dry pedantic killjoy, but he was probably watching a young calf drinking.
Re: (Score:3, Funny)
*sniff*
I'm dry and pedantic now
Re: (Score:3, Funny)
Q: How did the <insert target cultural/racial/whatever group here> man die whilst drinking milk?
A: The cow sat on him.
Sorry, couldn't resist milking it for what it's worth
Re: (Score:3, Funny)
>white liquid that tasted so good
The first few brave adventurers were killed by bulls.
JBODs? (Score:2)
...why?
I'm sure there's a good reason, but... He's using dtrace, right? Thus implying Solaris? Thus implying ZFS?
If you've got ZFS, why would you do JBOD?
Or did I just mis-hear him?
Re:JBODs? (Score:4, Informative)
A few reasons.
Parent
Re:JBODs? (Score:5, Informative)
Parent
Re:JBODs? (Score:5, Interesting)
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.
Parent
Re: (Score:3, Insightful)
Or did I just mis-hear him?
"JBOD" in this context will be a reference to the style of disk array (eg: vs one with a RAID controller like the Dell MD3000), not the ZFS RAID level.
Is this a feature? (Score:2, Funny)
Might the the drives themselves be sensing the induced vibration via an embedded accelerometer and momentarily parking the heads to avoid damage? It seems like the marketing folks shouldn't have too hard of a time putting a positive spin on this behavior.
A rack full of disks (Score:2)
if expressed with sufficient volume in front of a rack full of disks
I wonder about the results of eliminating the superfluous "full of disks" part.
Interestingly enough, it's precisely here, where the omission would both be understood and not bring unwanted connotations.
Great.... (Score:4, Funny)
Re: (Score:2)
You might like Accelerando by Michael Stross.
Sentient corporations and financial instruments and lawyer bots abound. It's a great book.
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Hard-drives as microphones?` (Score:2)
Nice, now I can use this to detect if people were loud in my server-room.
Do they also react to smell?
It's the Enclosure (Score:2, Interesting)
Secret Fact : Ultrasonic noise at low volumes ! (Score:5, Interesting)
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.
Re: (Score:2)
>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.
For starters, make an account.
Re:Secret Fact : Ultrasonic noise at low volumes ! (Score:5, Informative)
You don't know too many greybeards do you? I'm surprised that modern drives are susceptible to ultrasonic under 80 khz but real old drives and drums were known to have problems with low audible frequency harmonics. A simple solution to this problem is stamp a butterfly like pattern in the arm of the head. The same thing works for power lines (which is what the small dumbbell looking things are near the insulators)
Parent
Re:Secret Fact : Ultrasonic noise at low volumes ! (Score:4, Informative)
Informative? Seriously? I hope this is some metamod effort at providing Karma... but just in case someone does take this seriously, I should take out a patent on this. That way, when Monster sells their butterfly-patterned head arms for 20K to audiophiles who don't like the lack of warmth in SSDs, I can get in on the racket.
Parent
On colors of sound (Score:2)
White noise is just like white light: An even distribution of energy across the spectrum.
It makes perfect sense that white noise is less of a problem than an equal amount of noise at a specific frequency. Given a suitable frequency the material absorbing the energy will vibrate and even resonate. (That particular engineer's yelling, apparently, resonates well with the disks in the array of that video...)
It's the same reason why a bullet-proof west can make the impact of a bullet non-lethal: Spread out distr
Re: (Score:2, Funny)
And are those kept near the nuclear wessels?
Sorry, could not resist.
Also by Brendan Gregg (Score:5, Funny)
Also from Brendan Gregg comes the always useful /usr/bin/maybe [brendangregg.com]. Other funnies from him here [brendangregg.com].
before making fun of hard disks (Score:3, Funny)
the disk whisperer ... (Score:4, Funny)
I dub this guy the disk whisperer ...
What about my 300W Sub (Score:2)
That thing can shake my whole apartment. Is anyone testing what effect this thing has on my hard drives when listening to music/playing a game?
Disk Drives have a resonant frequency (Score:5, Interesting)
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.
Re: (Score:3, Interesting)
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 ventila
Re:White noise or not, it's the volume (Score:5, Interesting)
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.
Parent
Re: (Score:2, Insightful)
because all server admins are busy 24/7?
Server Admins are getting paid to 'watch' the servers. They have plenty of pseudo-free time. It's when stuff is breaking that they're busy. Not to mention a good admin in large server area will have software like that person had to watch drive latency.