OT - I'm curious - HDs and altitude

Ok,

 

I've read numerous times that hard drives are a lot more susceptible

to failure above 3000m altitude (roughly 10000ft). And numorous posts

here suggesting that people who are traveling to places that are

3000m+, should use a portable CD/DVD burner, rather than a portable HD.

 

So how is it that, when I went to Tibet in 2001, and spent most of my

time in Lhasa (3700m) there were quite a few net cafes? And no

problems with using the computer or getting online (except for the

sites that the Chinese govt censored).

 

I know about the effects of altitude, lesser air pressure etc, on HDs.

I have a degree in climatology, but they never covered the HD situation.

 

Why is it that a desktop PC will work fine, but a PHD is prone to

failure? What about a laptop - will it work or not?

 

Apologies in advance, but I'm going to capitalise the next sentence.

 

I AM NOT LOOKING FOR RECOMMENDATIONS ON WHAT TO BUY. SO PLEASE DON'T

OFFER THEM.

 

I'm merely curious.

 

Craig

The only thing that I can think of is that the heads in a HD "fly" on a layer of air that keeps them just above the surface of the platters. With lower air density, and less lift, they may fly closer to the platters and sometimes contact them. A marginal condition like this would create more problems with a HD that was being moved around in a portable device. Just my guess.

Of course it is possible to make PCs (and HDs) that work reliably at high altitudes. It's just that those in Tibet are likely to be such, while yours might not.

The advice that I've heard is that standard hard drives, although rated only to 10000 ft or so are perfectly fine at higher altitude as long as they are not being jostled or moved. My experience bears this out and I had no problems at higher altitudes up to 14000 ft.

 

I don't know about tibet, but in peru they had many internet cafes at high altitude. Since the country is so poor I doubt that they used special hard drives.

Hard drives are not sealed - if you look carefully, there is a little vent to allow air in, with a spiral chicane so that dust cannot work its way onto the platters. The heads float on a cushion of air, and the thinner air at high altitudes probably makes this harder. Which drives will fail or not probably depends on manufacturing tolerances more than anything else.

Hard drives (desktop, laptop or otherwise) are hermetically sealed at 1 atmosphere pressure, so the air pressure does not decrease significantly inside them with altitude.

<p>

However, the case may flex slightly because of the difference in pressure, and this might cause problems. I have no idea if high altitude actually does this, but some of the people in my department who spend time <a href=http://www.uncw.edu/aquarius/>here</a> at about 2.5 atmospheres have killed laptop hard drives. I think one faculty member has killed three or four. The NOAA people who spend more time there sometimes drill tiny holes in the drive case to allow pressure to equalize.

Mark, I think Fazal is right. At least it certainly looks to be a labyrinth air intake on all the desktop pc drives I've looked at.

All that I can add to what has already been said is that in my last job (retired now) I used a Dell Latitude notebook on over 60 commercial flights (typically at 30K -35K feet) without any hardware failures whatsoever.

<blockquote>

<i>"Another common misconception is that a hard drive is totally sealed. A hard disk drive

requires a certain range of air pressures in order to operate properly. If the air pressure is too

low, the air will not exert enough force on the flying head, the head will not be at the proper

height, and there is a risk of head crashes and data loss."</i>

</blockquote>

 

<a href="http://en.wikipedia.org/wiki/Hard_disk">

http://en.wikipedia.org/wiki/Hard_disk</a>

Commercial airline flights don't apply, because the cabin is presurized.

 

My guess is that there is enough tollerance to allow them to work most of the time, but some don't make it, and others don't if moved about while spinning.

 

There was an article here on photo.net that described a climber using one to back up his camera, and as long as he kept it completly stable everything worked, but this was only at altitudes marginally higher than the recommended limit.

I guess I stand corrected. However, that leaves one mystery unsolved: what's killing our hard drives?

Some good answers, but it still seems to be a mystery. :-)

<I>Some good answers, ...</I><P>

 

I disagree. I would characterize the above as speculation. <P>

 

For answers you need to go to the drive manufacturer and look at drive specifications. There

you'll find environmental specs listing the max altitude the manufacturer will guarantee

proper operation of the drive. As an example, Western Digital's 320 GB drive is spec'd to a

max operating altitude of 10,000 feet (and up to 40,000 feet non-operating).

Being at 40,000 feet on a commercial flight doesn't constitute being at that actual atmoshperic pressure, unless someone cracks open a window ;)

I know you don't want a recommendation but I Googled the Panasonic Toughbook (notebook pc) just to see what it's rated for and they give it a 15,000 ft altitude rating. They site some standard that military and other industrial-strength PCs use - MIL-STD-810F. You may want to Google that and see what some of the manufacturers use that meet this standard. Obviously *something* works at those altitudes; I'm sure the US military in Afghanistan encounters altitudes >10,000 feet and need PCs and laptops to keep on truckin'.

<i>Aaron W. , sep 17, 2005; 01:40 p.m.

All that I can add to what has already been said is that in my last job (retired now) I used a Dell Latitude notebook on over 60 commercial flights (typically at 30K -35K feet) without any hardware failures whatsoever.</i>

<p>

<p>

The aircraft you were in had presurized cabin. That is the air-presure in the cabin was held at a level that was much higher than the ambient air-presure you find at FL300-350. I'm afraid your experience isn't relevant because of that fact. We all do appreceate well intentioned input here at photonet. Even input with spelling errors (I usualy sneak in 1 or 2 dozen per posting, you want have to look hard to find them.)

My hunch is that the heads do not "fly" over the HD disks, or platters, with little wings

usiing the air as lift. What is meant by "fly" is that they hover very closely to the surface of

the spinning disks, close enough to read the magnetic state of the surface, or to write on

it. The word "fly" is used because it is unlike a record player needle, that drives right on

the surface of the old-style record disks. There is no need to use air to hold them up,

when the arm that the reader is suspended on his strong enough for the job. If it indeed

flies, how would you explain the hard drives that are positioned vertically?

 

that being said, I bring my PowerBook laptop to Quito, Ecuador, which is at 10,000 feet.

No problem with it. I think the risk is that they can get too hot -- less air to conduct away

the heat. I also had with me up there a Bigger Disk 1.6 terabyte HD. It worked great, but

now and then the fan would fire up to cool it down. I was a little nervous about that one...

I believe they do indeed "fly." Everything I've read states that they do. The heads are aligned so that they rest very softly (or very nearly so) on the surface of the HD platter. The spinning platter creates a wind that forms a high pressure cussion between the head and the platter. This cussion keeps the head off the surface of the platter, sort of like a tiny hovercraft.