kern/140752: [ata] [patch] [shutdown] HDD power-off procedure is not clean

[arundel at FreeBSD.org]

Synopsis: [ata] [patch] [shutdown] HDD power-off procedure is not clean

State-Changed-From-To: analyzed->patched
State-Changed-By: arundel
State-Changed-When: Mon Oct 25 20:44:55 UTC 2010
State-Changed-Why: 
Patched in HEAD (r214279).

Please note: This fixes the spindown issue only for ATA devices running under
CAM with ATA_CAM enabled. Fixing it for the ATA subsystem will require much more
work, since ATA in general has problems with power management. Since the ATA
subsystem will very likely become legacy software in the near future there are
no plans porting these changes to it.

There are plans of reworking mavs original spindown patch (r203420) at some
point in the future so non-ATA devices will benefit from it too. However for
this to happen the CAM subsystem needs some intensive improvement.
For now this commit poses an efficient way of preventing ATA hdds from dying
early due to exessive emergency head unloads/parks.

http://www.freebsd.org/cgi/query-pr.cgi?pr=140752