| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1062.1 | Who knows??? | WJG::GUINEAU | W. John Guineau, RD Buyout engineering | Tue Jan 12 1988 15:33 | 30 |
|
I think this is a somewhat controversial issue...
Any electronic device undergoes stress when powered up/down.
when a disk drive (at least RD type class) is "off" it's heads
are resting on the media. When it powers up, the heads ride on the media until
sufficient air flow allows them to "fly". So there is some additional wear
and tear here. Also, some disk's use whats called "thin film media" which
has a funny lubricant. This media is succeptable to "stiction" - the heads
get stuck to the media! Although modern technology is curing this, it exists
over some small population and is usually aggravated by loooong periods
of being "off" (ie heads on media). RD54 has this stuff and we have
done both long term shelfing and start-stop testing (I believe 40-50,000
start-stops and keeps on ticking...)
In general, I guess its up to you. Way the possible effects agains noise/power
consumption and then take a good guess :-)
All disk devices (and other things as well) have an MTBF (Mean Time Before
Failure) associated with them. This means that after some time (typically 15 -
30K hours) a drive is expected to fail (although we've seen 40-50K in reality)
Hope this helps!
John
|
| 1062.2 | | DICKNS::MACDONALD | WA1OMM Listening 224.28 | Tue Jan 12 1988 17:04 | 1 |
| FYI 40K hours MTBF is approximately 4 1/2 years.
|
| 1062.3 | Don't spin down Winchester Disk Drives | COOKIE::WITHERS | SN*W is a 4-letter word! | Wed Jan 13 1988 15:03 | 33 |
| It is in general a bad idea to spin down winchester drives of any
kind. This is due to seeral factors:
1) When drives spin down the heads land on the surface. There is
a measurable probablility (albeit small) that the heads will land
too hard - basically a head-crash (contact event as its known in
the trade).
2) There is lubricant on the surface of the platter. In some cases,
the heads may stick in the lubricant (stickision) and have bad
consequences as the drive spins up.
3) Because of the centripital forces, the lubricant will migrate
to the outer edges of the platter. After a long time, there may
not be sufficient libricants to prevent the heads from doing damage
on landing or takeoff.
4) The lubricant may glob causing a bumpy ride down for the heads
- essentially not good for the heads.
In the for what its worth department:
MTBF is the MEAN time to failure, not how long it will take for
YOUR unit to fail. It is a statistic that is derived from the
behaviour of the population of units. 40K hours says that you have
a probability of one failure in an average of 40K drive hours. Some people
may see lots of failures early in the life of the products. Other
owners will not see a failure ever. Put another way, if you have
4 drives with a 40K Hr MTBF, you can EXPECT a failure on the AVERAGE
of once every 10K hours.
BobW
|
| 1062.4 | what about power failure? | CIMNET::KYZIVAT | Paul Kyzivat | Wed Jan 13 1988 21:19 | 7 |
| I understand the merits of leaving the HD running, but how does one trade that
against the risks of damage from a nasty power failure? Is it possible to get
power conditioners (cheaply) which shut down and wait for manual reset after the
first power failure? I think that would be the best strategy for a home
computer, at least the way I use it.
Paul
|
| 1062.5 | | WJG::GUINEAU | W. John Guineau, RD Buyout engineering | Thu Jan 14 1988 11:36 | 14 |
|
I agree with this 100%.
When a drive is powered down, it's heads are parked WHERE NO USER DATA IS
LOCATED.
When a drive is left spinning, the heads can be ANYWHERE. If the
drive/controller don't properly handle power failure (and bad glitches etc...)
then there is a MUCH greater potential for data corruption than if the drive
is powered down.
John
|
| 1062.6 | Will Parking help | AITG::WISNER | | Thu Apr 07 1988 16:33 | 3 |
| With the SupraDrive they recommend "parking" the drive head before
moving the drive. Would it be worth it to run "PARK" everytime
a shut the power off?
|
| 1062.7 | | WJG::GUINEAU | | Thu Apr 07 1988 16:48 | 5 |
|
Most drives park themselves at power down
John
|
| 1062.8 | ? | NAC::VISSER | | Thu Apr 07 1988 16:50 | 3 |
| re.: -1
Oh, really? Which ones do? Do you mean most types of drives,
or most of the installed base of drives?
|
| 1062.9 | | WJG::GUINEAU | | Fri Apr 08 1988 02:22 | 14 |
|
Winchester drives in general.
Of the several RDxx drives DEC sells (RD52,RD53,RD54,RD31,RD32,RD33)
only one (RD31) must be manually parked.
The basic method used is to re-direct the back-emf generated by the
spindle motor into the voice coil actuator to drive the heads
into a "landing zone"
John
|
| 1062.10 | Didn't see any parking... | VTHRAX::KIP | Explain the Universe and give 3 examples. | Mon Jun 13 1988 18:31 | 6 |
| I've watched the head motor as I've removed power from an RD50 and RD51 hard
drive...neither one seemed to automatically "park"; however, both did move the
heads to an intial position (track 0?) when I *applied* power to them. Note
that I did not have any controller connected to either when I did this test. I
would have tested an RD52 but am not sure where to look to detect head movement.
|
| 1062.11 | disk drives | WJG::GUINEAU | | Tue Jun 14 1988 11:26 | 47
|