Re: Spinning down sata disk before poweroff

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sat, Jun 18, 2016 at 09:54:02PM -0500, David Young wrote:
> On Sat, Jun 18, 2016 at 10:51:25PM +0200, Manuel Bouyer wrote:
> > On Sat, Jun 18, 2016 at 03:31:20PM -0500, David Young wrote:
> > > BTW, what should we do during "manual" action, such as 'drvctl -d wd0'?
> > > Seems like we should power off the drive then, too?  Otherwise, it is
> > > set up for an abrupt power-loss, later.
> > 
> > But if you do this in order to do a rescan, you will power down/up
> > the drive, which is not so good for enterprise-class drives (for drives
> > designed for 24x7 SMART counts the number of stop/start cycles)
> 
> I don't understand.  Why detach in order to do a rescan?

You can't rescan if there is any device attached to an atabus
(you get EBUSY).
In such a case you can put the device in standby with atactl before
detaching.

> 
> BTW, I think that when I wrote "power off the drive," I should have
> written "put it into standby."  I'm not sure the formal meaning of
> standby, but I reckon it is up to the drive (controller?) whether or not
> to stop the spindle as well as parking the heads.
> 
> Seen in a certain perspective, it's asymmetric that frequently the
> BIOS powers a drive *up* before the bootloader runs, but the OS is
> responsible to power a drive *down* during power off, or else the drive
> may abruptly lose power.  Is there some way to hand responsibility for
> the drive's power state back to the BIOS?  I guess that on x86, that
> would be an ACPI BIOS method.  Don't we use an ACPI method to power down
> the machine, after all?  ISTR we put the machine into "sleep state 5".

No idea if there is an ACPI method for this. And this woudln't help
e.g. evbarm.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--