Are disk bearings really harmed by spin-up?

[Folkert Rienstra]

Nope, nothing like it. The bearings are completely different,
you dont get anything like the spinup torque you get on a
hard drive platter with a car wheel, and the hard drive has

a single bearing on one end of the axle too.

Nonsense.

[snip]

 

[J. Clarke]

John... sounds like you know what you're talking about. So my question is:
In my Windows power scheme I have for years selected "Turn Off Hard Disks
= after 3 hours". I have never noticed this actually happening. Sounds
like you would suggest turning this option off.
Possibly I don't notice the drive spinning down is that I seem to have
fairly constant network activity. I have a DU meter that monitors the
network and it pops up more often than every 3 hours. So maybe my 2 drives
are not "turning off".

In practical terms it makes little difference. Disks are rated for a certain
large number of start-stop cycles--WD Raptors for example are rated for
20,000. If you're running a server it's unlikely that it's ever going to
be idle long enough for the disks to power down.

 

[Randy S.]

Indeed. That is possibly an other factor.

Personally in my PC servers I go for PSUs that can take the full
spin-up load of all disks at once. That has the advantage that during
normal operation the PSU is not under higher load, which should
increase its lifetime. The limit for this is somewhere around 10-15
disks, since PSUs with more than 550W are dificult to get.

Most client PC's don't have any need for staggered spin-up, so I'd
totally agree with you. It's only in good size servers with lots of
RAIDed drives that it's really an issue.

Randy S.

 

[J. Clarke]

In principle it's the same, just with a lot more load on those wheel
bearings. They take a lot of stress when you drive so I question that
pulling out of the garage is significantly worse than a long trip on a
hot day. Cold engine starts are different because oil has to be pulled
up farther from the crankcase, though there's usually film left on the
cylinder walls and crank bearings. Slick 50's claims of metal on metal
are overhyped. But this is getting off topic.


Other posters have claimed that power usage is nil but clearly it's
not. My main angle on this was about saving energy. Multiply 5 watts by
millions of computers and you've saved a lot of power. Do that with
countless other gadgets and you've saved a lot more. People leave work
monitors on all weekend (with goldfish tank displays) when they're
gone. Too much trouble to push the off button or let the screen blank
out? Diesel owners idle their engines way too much, etc..

Anything that doesn't have to run 24/7 could be turned off instead of
blaming it all on Kenneth Lay and the Arabs.

You wanna see _waste_, go outside tonight and look up. And every single one
of those is blasting enough power into space in a single second to run all
of human civilization at its current level for about a million years.

 

[Randy S.]

You wanna see _waste_, go outside tonight and look up. And every single one
of those is blasting enough power into space in a single second to run all
of human civilization at its current level for about a million years.

This thread is taking some odd turns! I'm not sure it's relevent to
call the physics of stars waste. I would reserve that term for
excessive use of limited available resources.

Randy S.

 

[Eric Gisin]

This thread is taking some odd turns! I'm not sure it's relevent to
call the physics of stars waste. I would reserve that term for
excessive use of limited available resources.

Energy is not a limited resource. Our planet receives orders of magnitude
more than we need. Over 100e15 watts.

 

[Alexander Grigoriev]

When a lightbulb's filament is cold, its resistance is a fraction of its
operation resistance, because for pure metals, resistance about linearly
changes with absolute temperature. This causes initial overcurrent which may
burn a weakest spot of the filament. When this happens, an arch may form in
the argone gas, this is why one of conducting wires also usually melts.

 

[Alexander Grigoriev]

Considering that the HDD's bearing must be very tight (probably with
sub-micron play), in what ways do you think such tightness affects the
bearing's operation during startup and in steady mode?

 

[J. Clarke]

When a lightbulb's filament is cold, its resistance is a fraction of its
operation resistance, because for pure metals, resistance about linearly
changes with absolute temperature. This causes initial overcurrent which
may burn a weakest spot of the filament. When this happens, an arch may
form in the argone gas, this is why one of conducting wires also usually
melts.

Have you ever noticed that sometimes you can fix a light bulb by giving it a
light tap so the filament ends touch? Sometimes they'll weld if you do
that and it will run a while longer.

 

[J. Clarke]

This thread is taking some odd turns! I'm not sure it's relevent to
call the physics of stars waste. I would reserve that term for
excessive use of limited available resources.

All resources are limited. Eventually it's _all_ going to run out, every
single bit of it. If stars weren't burning it so fast it would last a lot
longer. The solution, if we can't turn the stars off, is to enjoy it while
it lasts, because anything that _we_ do to save is negligible.

 

[Randy S.]

Considering that the HDD's bearing must be very tight (probably with
sub-micron play), in what ways do you think such tightness affects the
bearing's operation during startup and in steady mode?

I was being very general. Fit tolerences had large effects in bearings
that I used to design because often the inner race, outer race, and
bearing elements were all manufactured from different alloys (usually
titanium alloys, steel alloys and sometimes nickel or aluminum alloys).
The thermal coefficient (alpha) of these materials varied enough that
fit tolerences would change significantly as temperature changed.
You're correct that the fits are fairly tight (though *far* from
sub-micron, I think you're thinking of the bearing and race finishes,
which must be that close. Submicron fits wouldn't allow room for
lubrication movement, or even movement at all!), which *exacerbates*
thermal effects.

With HDD bearings, the inner and outer races are almost certainly the
same material, so thermal changes wouldn't change their fits, though the
bearing elements probably have some variation. Also, I was typically
working with thermal changes of 500 deg. F and up, HDD's only see a
delta of 100 degrees or so, so that would make it less significant.

Randy S.

 

[Jason]

Yes, one boot per day would be negligable, and wouldn't really be a
factor. But power saving modes could increase that a lot. If your HDD
powered down after 10 minutes of idle time (not unrealistic for a laptop
trying to save battery), it may cycle 40-50 times per day easily. So if
you divide 109 by 50, that's only a little over 2 years! Of course this
is an extreme case, and, as was noted in another post, notebook HDD's
are often engineered for more start/stop cycles. The thing to note is
that it *is* a design criteria. The other thing to hope is that as
desktop PC's become more power conserving, the HDD's had better be
designed for higher start/stop cycles.

Randy S.

Both of you completely missed an important word that occurred
multiple times in that link, 'Minimum'. Read this paragraph
again:

For this reason, hard drives are given a specification for the
minimum number of start/stop cycles they are designed to handle
during their service life. The value for a desktop drive is
typically between 30,000 and 50,000 cycles (and remember that
this is not an average, but a minimum). Notebook drives, which
are more commonly spun up and down a great deal to save battery
power, usually have even higher numbers.

Find something that starts quoting the engineered specs for both
lower and *upper* limits, and that will be a usable set of data.


And until TiVo decides to incorporate an option to spin down the
disk between scheduled recordings, it doesn't matter anyway.
I hope they never put in such an option, because there have been
plenty of times that 30 minute buffer has been astoundingly
useful. For example, a few days ago when that 2-seater cessna
flew over washington d.c. I walked into the room and saw people
running down the street. 'What the hell?', I think; and rewinding
10 minutes gives the story.

 

[Jeff Rife]

(Jason) wrote in alt.video.ptv.tivo:

I hope they never put in such an option, because there have been
plenty of times that 30 minute buffer has been astoundingly
useful. For example, a few days ago when that 2-seater cessna
flew over washington d.c. I walked into the room and saw people
running down the street. 'What the hell?', I think; and rewinding
10 minutes gives the story.

That's why I want TiVo for real life. I could have seen it live if I would
have been able to back up 30 minutes and go outside.

 

[Randy S.]

Both of you completely missed an important word that occurred
multiple times in that link, 'Minimum'. Read this paragraph
again:



Find something that starts quoting the engineered specs for both
lower and *upper* limits, and that will be a usable set of data.

I really have no idea what point you're trying to make. Of course, it's
a minimum, that what you design for in Engineering. That's because the
event you're trying to avoid is usually catastrophic (to the device at
least), and it doesn't really matter how long it *could* last, but how
long you can *count* on it to last. It's useful for me to know that I
can count on 99% of HDD's to operate 5 years of normal operation without
failing (I'm making that number up, but you get the idea), because then
I can infer a replacement interval or life cycle. It does me no good to
know that 1% of HDD's could operate 20 years, because there's no way of
knowing *which* 1%!

The only time I can concieve of engineering a "maximum" life is for a
operation limiting part, perhaps to serve as a wear warning. But that
is really uncommon.

And until TiVo decides to incorporate an option to spin down the
disk between scheduled recordings, it doesn't matter anyway.
I hope they never put in such an option, because there have been
plenty of times that 30 minute buffer has been astoundingly
useful. For example, a few days ago when that 2-seater cessna
flew over washington d.c. I walked into the room and saw people
running down the street. 'What the hell?', I think; and rewinding
10 minutes gives the story.

Well, I like the live buffer too, plus, as I think we've already reached
a consensus on, the significance of full time operation of the HDD in a
Tivo is probably close to nil.

Randy S.

 

[RPR]

FWIW, the startup current causes a lot of stress in the drive
electronics too, especially the power circuitry and motor drivers. I
remember electrolytic caps blowing when you power cycled certain drives
too often. That may be less of an issue today than in the good old days
of many-platter 8" and 5.25" drives, but the electronics got smaller
too so it definitely gets stressed. Also, unless you have ramp loading
(which has its own set of issues), the heads get thermally stressed
through friction, in addition to the mechanical stress.
I leave my drives on 24*7.

 

[Howard]

Well, I like the live buffer too, plus, as I think we've already reached
a consensus on, the significance of full time operation of the HDD in a
Tivo is probably close to nil.

I don't know if I would say that. The 'it's wasting energy!' people would
(and will...most likely within a week at the rate they have been going
lately) say it is a very high significance. They keep desperately reaching
for some other, more valid excuse though, and try to say you are doing no
harm by turning the device off. As we've all seen (many many times over
now, it surely is getting old) this not only keeps you from using the
device as it is intended, you ARE, in fact, doing harm.

Someday, they'll get a clue that it's not a 'waste' when I'm using the
energy IN THE EXACT WAY I WANT TO.

Ok, no they won't, but I can dream.

 

[Randy S.]

@spnode25.nerdc.ufl.edu:




I don't know if I would say that. The 'it's wasting energy!' people would
(and will...most likely within a week at the rate they have been going
lately) say it is a very high significance. They keep desperately reaching
for some other, more valid excuse though, and try to say you are doing no
harm by turning the device off. As we've all seen (many many times over
now, it surely is getting old) this not only keeps you from using the
device as it is intended, you ARE, in fact, doing harm.

Sorry, you're right, I meant to say that it as little significance to
the *reliability* of the device. Power savings are a different matter.
I wasn't precise enough ;-)

Randy S.