Formato de Bajo Nivel y Discos Muertos (Was: Re: Cortar por lo sano (Re: disco externo y live-cd...))

[Alvaro Herrera]

Horst H. von Brand escribió:
> Juan Manuel Doren <jm.doren en ok.cl> wrote:
> > googleando un poco encontre una explicacion que me parece la mas sensata
> 
> > el aire a mayor altitud es menos denso, eso hace que le de menos
> > soporte a los cabezales del disco. disminuyendo la distancia entre
> > estos y la superficie del plato.
> 
> Los discos estan hermeticamente sellados (porque incluso una particula de
> humo puede provocar un aterrizaje forzoso del cabezal, por la minima
> distancia entre este y la superficie). Si no lo estuvieran, por los cambios
> de presion (cambios climaticos, altura, ...) entraria basura.

No están sellados herméticamente! Sólo hay un filtro en el paso de aire.
No encuentro una referencia buena, pero por ej.
http://www.pbcomp.com.au/hard-disk-backup-recovery.html
"Looking inside a Hard Drive" dice:

	The hard drive enclosure relies on air pressure inside the drive
	to support the heads at their proper flying height while the
	disk is in motion. A hard disk drive requires a certain range of
	air pressures in order to operate properly. The connection to
	the external environment and pressure occur through a small hole
	in the enclosure (about 1/2 mm in diameter), usually with a
	carbon filter on the inside (the breather filter, see below). If
	the air pressure is too low, there will not be enough lift for
	the flying head, the head will not be at the proper height, and
	there is a risk of head crashes and data loss. Specially
	manufactured sealed and pressurized drives are needed for
	reliable high-altitude operation, above about 10,000 feet (3,000
	meters).

Huh, la Wikipedia tiene un texto extrañamente similar:
http://en.wikipedia.org/wiki/Hard_drive
	The HDD's spindle system relies on air pressure inside the
	enclosure to support the heads at their proper flying height
	while the disk rotates. An HDD requires a certain range of air
	pressures in order to operate properly. The connection to the
	external environment and pressure occurs through a small hole in
	the enclosure (about 0.5 mm in diameter), usually with a carbon
	filter on the inside (the breather filter, see below). If the
	air pressure is too low, then there is not enough lift for the
	flying head, so the head gets too close to the disk, and there
	is a risk of head crashes and data loss. Specially manufactured
	sealed and pressurized disks are needed for reliable
	high-altitude operation, above about 3,000 m (10,000 feet).

-- 
Alvaro Herrera                               http://www.PlanetPostgreSQL.org/
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