RE: SCSI disk spin-down/up

Bryn Paul Arnold Jones (bpaj@gytha.demon.co.uk)
Thu, 29 Feb 1996 02:24:12 +0000 (GMT)

On 28 Feb 1996 Ray_Van_Tassle-CRV004@email.mot.com wrote:
> * "power off" is a LOT different from "spin-down with power on". For one
> thing, the drive assumes room temperature. With power applied, there is
> certainly heat in the drive case.
Why so, Spinup from cold is diffent, but spin up from walm, wether from
a hard reset, a spindown, or poweroff (but hasent cooled down yet),
shouldent cause problems, or why would the drive manufactures allow it ?
They could have a jumper that sets wether the drive quitely acts as if
it's spinned down, but keeps going, with warnings in the docs that making
the drive to spindown can shorten it's life, or no jumper, just act this
way anyway.

> * The "stiction" is claimed to be from lubricant migrating to the area
> between the heads and the platters, and creating enough grab (surface
> tension?) so that the spindle motor can't start the platters spinning.
> Warm/hot lubricant will certainly flow into this critical area much
> easier than cold lubricant.
I'm sorry, but if lubricant can get to the drive heads, and cause
sticking, it's an inherently broken design in my book. I don't see that
even allowing the posability of a lubricant (except air) to get to parts
that are microns from a suface that is moveing at 24.6 miles an hour
(11.0 m/s, or 7/2 * PI m/s) on a 3500rpm drive, and 50.6 miles an hour
(22.6 m/s, or 36/5 * PI m/s) on a 7200rpm drive, all at 1.5" (3 cm) from
the spindle.

> And finally:
> * If there is a significant chance of messing up a disk drive, why take that
> chance? Manufcaturers rate the running MTBF, and the number of stop/start
> cycles, but AFAIK *NOT* the "spun down with power applied" time. It's quite
> possible (likely?) that the drives are NOT designed or certified or tested
> for operation this regime.
>
Ok, they don't quote figures for it, but they still program the drives to
react to a spindown command, if they really thought that it's a very bad
idea they'd just have the drives ignore the commands to spindown. (yes I
am repeating my self, and consusly (?sp) so).

> -30- Ray
>
Bryn

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